I was trading these 3 or 4 months back along with a few friends, and we all had the same experience. We'd enter an ATM IF with $50 wings in SPXW.X a few minutes after the cash open, then put in a limit order for 8-10%. Usually took less than an hour, and since we were trying to figure out how it worked, we'd literally sit and watch them. I don't remember ever getting filled at nat; usually somewhere around 0.07 past it, sometimes as much as 0.10. I though that it might be something with TradeStation, but the other folks were using TW and had the same experience.
I tried legging out at one point; got better fills, but it was a mess if it went against you.
I tried legging out at one point; got better fills, but it was a mess if it went against you.