You make a very good point, which I totally agree with. I am personally uncomfortable with allowing a position to remain open for up to say 696 pips as the EU did in the data I put together on that pair. No matter whether I examine a dozen fx pairs and they all show 100% gap closure, I could not allow a position to remain open to that level of swing based on my broader trading principles, and I would not advocate anyone do that. But it is handy to know the actual stats on a trade opportunity like this - just part of DYOR.
An example of your point is the BOJ decision to weaken the Yen this week - if something like that happens, or say the RBA increases its rate - it basically re-rates the currency and any gap opened prior to that may never get filled due to a fundamental shift in foreign exchange policy.
Monday gaps does not form the only part of my trading or even fx trading, but I'm doing my research to determine how reliable it is as a trading opportunity, what the average gap size really is (as opposed to anecdotal comments), obtaining a better understanding of currency movements in this particular regard but also in general, and finally to obtain some insights that am now seeing which I didn't before analysing this data.
As a result I have become more interested in the swings that can occur before gaps close, than the actual gaps, so that when a trend change occurs I can add the gap opening as a possible target in addition to any S & R levels that I would normally have added to my chart.
As for using only IG data, I only trade IG so I trade what is presented to me and that's the IG data, which represents the market that IG makes.
