Honestly I think the grain variability issue comes down to the crush and hence efficiency. But the crush is hard to control. I struggled with that some too, actually got a #14 sieve and tested gap settings. Ended up with a much tighter gap than I anticipated and have had no sparging issues, and saw ~10% jump in efficiency. This is why ssbrewtech's new grain mill is tempting me, easy, on-the-fly mill gap adjustments. I've been too lazy to try and adjust the mill gap for different grains, but I wouldn't be surprised if the extraction decrease you saw with Crisp Maris Otter wasn't at least partially crush related. Based on my sieve test it's extremely hard to just look at the crush or run your hand through it, and know if it's dialed in. Though efficiency is the true indicator.
Yeah, I have my profile default at 1.5 qt/lb, and I'm planning to keep that constant as I test out some batch sparges. If I go back to fly sparging I would do 1.75, and hold that constant.