A payoff diagram can be exact while its entry price is unrealistic. Multi-leg orders combine several markets, and each quote has a bid, ask and timestamp.
The midpoint is a reference, not a fill
The midpoint is halfway between bid and ask. It can be useful for comparison, but no market participant is obligated to trade there. A displayed last price may be older than the current quote and may describe a different market condition.
For a debit position, buying near asks and selling near bids makes the executable debit worse than a simple collection of midpoints. A combination order may improve the result, but fill quality remains uncertain until executed.
Convert quote friction to position dollars
A $0.10 quoted width usually represents $10 per standard 100-share contract before quantity. Across four legs, seemingly small widths can materially change expected P/L. Do not blindly add full widths as a forecast; instead test an explicit slippage assumption and compare it with the strategy’s profit target.
Volume and open interest do not guarantee a narrow spread or immediate fill. Inspect current two-sided quotes for every exact contract.
A useful limit-order process
Verify the complete contract identifiers, use a net position limit, and avoid treating an unfilled order as evidence that the theoretical value is wrong. If the price must be chased beyond the research budget, the trade has changed. Record the actual net fill separately from the pre-trade estimate.