In my opinion, the gap, by itself, doesn't provide any useful information
Gaps are a form of impulse and indicates an imbalance in trade. And for a day trader, being aware of the gap and where price is trading relative to the gap is
extremely valuable. Of course I am aware that not all gaps fill. But you ought to use
statistics rather than your opinion when it comes to analyzing the chances of a gap filling the day of the gap or not.
You can use a program such as excel, and use size of the gap to categorize various gaps, and also whether the gap is outside or inside the prior day's range, and then use a 15 minute opening range as a secondary data point; and from there calculate the odds of a particular type and size of gap filling the day of its occurrence when that gap hasn't closed during the first 15 minutes of RTH. Excel lets you track ORB breakouts, breakouts that trend, reverse, etc. Very flexible program and easy enough to learn.
That is information you can take to the bank. "In my experience," you say. Well, in my experience, our memories and the opinions produced by such memories are often very poor and thus often inaccurate reflections of reality.
This is an
information game. That is all technical analysis is - analyzing information. But most do not look at it as pure information. Most are looking for patterns but with no appreciation for the data that is building the "pattern." We somehow come to look at a price chart as something magical when it is no different than a chart that tracks the incidence of an infectious disease or the voting trends of baby boomers. It is all simply information.
Now, what information does it show, and what do we wish to be able to infer from that information? Ask yourself what any single data point at its smallest increment - the tic - represents in fact. Ask: "What
is price?"
Trend days themselves are worth tracking and study. So while you are at it, I'd suggest doing similar data runs of open <=> close using price relative to today's open and yesterday's close and using price at various intervals throughout the day to calculate how frequent or not these intraday U-Turns you imply might happen.
When I started tracking I bought years worth of historical intraday data and have since then kept it myself. That was several years ago. Perhaps there is a free source you could find today. The data was not cheap. Again, excel is a wonderful tool if you'd like to add mathematical statistical support to your odds calculation rather than opinion.
As far as the adage that "gaps always close," I'd not base a day trading plan on it, that's for sure.
I will tell you also that if you knew what I know, and what I know is based on nothing other than my having done some work that you have not, you'd see that chart you posted much differently than you do.
I'm not special. I'm not smarter. But with respect to intraday and day to day price action as it relates to the S&P 500 index and its derivative futures, I am simply more well
informed.