Max Position Size
Max Position Size is the cap on how much of the portfolio any single stock is allowed to occupy at a rebalance, expressed as a percentage of total capital. SledgeKey defaults to 10%, with the slider running from 2% to 25%. The cap matters most for weighting schemes that produce uneven sizes, like market cap or revenue weighting.
What is Max Position Size?
Max Position Size is the upper bound on the weight of any one holding in the portfolio. After the screen has chosen which names to hold, and after the weighting metric has decided how big each position should be, this cap is applied as a final check. Any holding whose computed weight would exceed the cap is trimmed back to the cap, and the trimmed weight is redistributed across the rest of the portfolio.
The setting is invisible when the weighting metric produces evenly sized positions. On equal weight with 20 holdings, every name is already at 5%, and a 10% cap never binds. Where the setting matters is the family of weighting metrics that produce uneven sizes, which includes market cap weighting, revenue weighting, and free cash flow weighting. These metrics size positions in proportion to a company-level value, and that value can vary by orders of magnitude across the portfolio. A megacap technology company can easily occupy 30% or 40% of a cap-weighted basket of 20 names without a cap, and the strategy's result becomes mostly a story about that one stock.
Practitioners sometimes think of Max Position Size as the diversification floor below which the strategy refuses to fall. It does not change which stocks the screen picks; it changes how much of your capital any one of those picks is allowed to control.
Why Max Position Size Matters in Backtesting
A backtest result is a blend of two things: how well the screen identifies attractive stocks, and how the chosen weighting scheme converts that selection into portfolio weights. Max Position Size pulls these two contributions apart. A loose cap, or no cap, lets the largest position in the basket carry most of the return signal. A tight cap forces the result to reflect the full set of holdings rather than the single biggest one.
This matters most when an investor wants to test a strategy's selection logic rather than its concentration profile. If the goal is to know whether the screen picks good names on average, the result needs to come from many positions rather than from a single dominant one. Without a cap on cap-weighted strategies, a flattering five-year backtest can be entirely the work of a single name like Apple or Nvidia that the screen happened to size into the top slot. The other nineteen picks contributed little to the headline number.
The cap also changes the strategy's risk profile in a way that the topline return numbers may not advertise. A 10% cap on a 20-name portfolio guarantees that no single failure can erase more than 10% of capital between rebalances, which puts a hard floor under single-stock blow-up risk. A 25% cap, by contrast, exposes the portfolio to materially more concentration. Both can be defensible. The point is that the choice is not cosmetic.
How SledgeKey Implements Max Position Size
Max Position is a slider in the backtest configuration panel. The slider runs from 2% on the low end to 25% on the high end, in one-percentage-point steps. The default is 10%, which is loose enough to let conviction-weighted strategies size up their best names while still preventing any single position from dominating the portfolio.
At every rebalance, SledgeKey computes what each holding's weight would be under the chosen weighting metric, then applies the cap. Any holding whose unconstrained weight exceeds the cap is clipped to the cap, and the clipped excess is redistributed across the other holdings in proportion to their current weights. The process repeats if the redistribution causes another holding to breach the cap, until every position fits under the limit.
Two checks before settling on a value. First, make sure the cap is consistent with the number of holdings. A 5% cap on 10 holdings can only fill 50% of the portfolio, leaving the rest in cash and creating an uninvited cash drag. As a rule of thumb, the cap should be at least one divided by the number of holdings: 1/20 is 5%, 1/10 is 10%. Second, remember that the cap interacts with the weighting metric. On equal weight, the cap rarely binds. On market cap weight, the cap usually binds aggressively for the largest names.
Common Pitfalls
The most common pitfall is leaving the default cap in place on equal-weight strategies and assuming the cap is doing protective work. It is not, because equal weight already enforces the same diversification the cap would. The cap is a real input only when it conflicts with the weighting metric.
A second pitfall is choosing a cap so tight that the portfolio cannot be fully invested. A 3% cap on 20 holdings leaves the strategy permanently 40% in cash, which mutes both gains and losses and creates a misleading volatility number. The strategy is technically running, but the cash drag is doing more work than the screen.
A third pitfall is comparing two backtests with different caps and treating the difference as evidence about the screen. Almost any well-known cap-weighted screen produces a higher backtest return with a 25% cap than with a 5% cap, simply because megacap leadership over the last decade rewards concentration. That is information about market regime, not about screen quality. Hold the cap constant when the question is about the screen.
On equal weight, or any weighting metric that already produces uniform sizes, Max Position Size does nothing. It is a real risk control only on metrics that produce uneven weights, like market cap, revenue, or free cash flow. Treating the slider as a universal safety knob is a common mistake.
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