Mash Duration and Sparge Method on FG

So, I've done quite a few all grain brews so far. My typical brew day is a single infusion mash then fly sparge with 185-190 degree water in a 10 gal cooler MLT with false bottom. I'm consistently getting about 75% efficiency. My first few beers I did my sparge with 170 degree water and my gravities were finishing where I thought they should.

I slowly started increasing the water temp as I brewed more beer to have the finished grain bed hit 168-170 degrees, hence the 190 degree water. Well, I noticed that since I've been doing this, my FGs were finishing a little higher despite better yeast practices. My reasoning is that I'm my unconverted grains are resting at progressively warmer temps resulting in a fuller final product. Would a longer mash cure this?

I could add another infusion of boiling water to mashout then sparge with 170 degree water. This seems to be pretty common, but would add another step to my day.

Is there much downside to going the other way and just sparging with water the same temp as my mash? I'm thinking this should keep the FG where I want it. I've never had issues collecting first runnings from my MLT so I'm not sure the warmer sparge water is even necessary.

How much higher are we talking abut? I'm not so sure that the higher sparge temps have anything to do with it at all... After all, by the time you are sparging, conversion should be completely finished.

not much... still within style but maybe 3 points on the high end of that range. I just know that my first few beer finished right where they should and now they're finishing a couple points higher than ideal.

Hw much roasted/specialty grain is going into these recipes? Are you going strictly by what your brew software tells you that your FG should be? If so, then stop paying a lot of attention to that... That is purely a guess, there are simply too many variables to make an accurate guess at what the FG should be.

Are you hitting your mash in temps properly? Try adjusting them down one to two degrees and see if that helps at all. Be careful when sparging with very hot water, you could possibly leach some tannins from the grains in the mash.