I'm lazy. I basically just pick a number, the 1600 close, since that's the market "close". But, you're right, I really ought to use 1615.
In any case, since this particular market doesn't really "close", it doesn't pay to be too rigid about gaps, which I was yesterday. I usually check the NDX, but didn't this time. Just goes to show ya.
If this seems to be too much "whatever feels good", a lot of these small gaps fill during off-market hours, especially in the early morning. Therefore, technically, they are no longer gaps. In fact, I tried for quite a while to base my early plays on what had happened before the open as far as support and resistance and candle lengths and so on, but I found that the whole gap thing is more psychological than arithmetic. In other words, if the market gapped, the futures would behave as though they had gapped as well, whether they had or not, and whether those gaps had filled pre-market or not. If the market didn't gap, then the futures would more likely be dull at the open.
Now you can see why gaps aren't a part of the strategy I posted; it's very difficult, at least for me, to come up with a set of rules that I can communicate to somebody. And without that, I'd rather consider gap plays as something separate. And I know that if I can't communicate the rules to somebody else that they aren't clear enough in my own mind, which is true. All I can tell you is that I'm still working on it and look forward to whatever findings others may come up with, even if they are only very tentative.
--Db