I was hitting 90% for a while, when I was crushing really hard. Then I wondered if such a high efficiency was causing my beers to taste thin and watered down, so I actually opened the gap on my BarleyCrusher. Now my average is around 82-85% (I don't have the exact numbers here at work). I still need to run some more experiments to know for sure whether high efficiency has any real adverse impacts on flavor. I think it does, but I'm not 100% certain yet.
My setup? Well... for starters, I am a small batch brewer, and I boil only on my electric stovetop. I do not own a turkey fryer or burner setup at all, never have and possibly never will. The efficiency numbers above apply primarily to my 2.5-gallon batches. At that time, my batches were split about 50/50 between BIAB and a blue rectangular cooler. Recently I've gone down to 1.7-gallon batches and so now I'm solely BIAB. I do indeed sparge most of my beers, unless making a small beer, then I skip it or else my efficiency will be >90% again and I'm concerned about that. To do a sparge, I either set the bag in a colander and pour hot water over it, or else I take the shortcut method and just dunk the whole bag in hot water. Either way gets me the efficiency boost to mid-80s that I like. Beyond that, everything is a pretty standard 50/50 first runnings to sparge ratio, heat my sparge water to 190 F like you do, etc. My mashes are just 40-45 minutes. This has always been good enough for me to get the high efficiency and attenuation that I like. If I mash longer, my efficiency and attenuation each increase by a point or two -- big friggin deal. I figure I might as well save 20 minutes of my life on every batch.
If you want to increase your efficiency numbers, the best advice I have is:
1) Crush harder than you think you should;
2) Split your runnings and sparge volumes 50/50;
3) Ensure you collect every last drop from both your first runnings before the sparge, and from the sparge runnings. If using a cooler, you must tilt the cooler upwards for a good 5-10 minutes and collect everything that comes out. Your so-called "dead space" needs to be very small, less than a quart. If for example you're leaving a gallon of dead space in there for both the first runnings and sparge, your efficiency is never going to get into the 80s. IF that matters to you. Which, it shouldn't...
My theory is that low efficiency actually makes a BETTER tasting beer than high efficiency. If I wasn't so dang cheap, I'd probably make a lot more no-sparge beers and just suck it up, set my standard efficiency at like 55% and be very happy with the flavor. So, don't be disappointed if your efficiency is low. You might in fact be making a better tasting beer than all the rest of your friends who get efficiency in the upper 80s.
More experiments are needed. Which I shall happily consume.