I don't actively trade for almost 2 years, but I remember live fills are much worse than paper. You can wait for hours to be filled between bid and ask in reality, while paper allows you almost always buy bid and sell ask.
No, the own limit price has to be hit or crossed by the market price for a fill. Meaning: it is the same mechanism in both paper and real. I can repeat: the IB paper account is very realistic; that's the experience I made 4 weeks long trading daily fulltime.
Just in case, count your P&L as if you paid the whole spread on every leg in and out. This will make it more or less realistic (except if you execute at market, which can slip).
I don't trade like many others, it seems. My goal is ideally to just open the position and let it expire, not actively close, reopen etc. etc. As I already wrote: I always use only limit orders, never ever market orders. I have my own P&L calculation, but the spread is not necessarily part of it. But of course the spread is part of my risk calculation.
Then just consider spread as if you paid it on entry legs. You have no underlying positions left after expiration ever?
Thx but I'm comfortable with the way I do. I assume you mean assignments. Sure that happens... But it's already counted-in in my method.
Emotional comfort is good, but you better play safe and know for sure what to expect when you go live. Believe me, surprises are mostly not pleasant. On paper account I always had perfect fills (not IB, faster futures platform, IB is terrible for quick fills actually), live I had some slippage on as low volume as 10 NQ contracts.
I told you: I don't use market orders, so slippage can't happen with limit orders... So, no surprises here... I'm using probabilities and "cushions", ie. using safety zones... But black swans can still cause problems, I know.
Unfilled orders you otherwise consider as filled and consequently, missed trades (ironically, the best of all), can.
I'm a patient person... Just apply maths, because the orderbook is like a "fair machine". I'm making use of it with the help of maths and probability... Example: if I put midprice then it has to be filled if market price hits/crosses it... Ie. under normal circuimstances it can't be ignored, skipped, jumped-over if the market crosses my price...