What's your secret to 80+% efficiency. I usually get 70-ish%.
The lauter efficiency for almost any batch sparge will be over 70%. If you get full conversion efficiency, then mash efficiency should only be under 70% for very big beers. So either you have a lot of dead space, or your conversion efficiency is low. That could be due to any one, or more, of the mash parameters (temperature, pH, crush, thickness, time) being out of its optimal range. Once you optimize all those parameters, efficiency should be very predictable.
My mash lauter is usually lower than expected and my sparge lauter is usually higher than expected.
This is a dead giveaway that conversion isn't complete at the end of the mash rest. Rest longer and see what happens, or try a psuedo-mashout at ~160°F before lautering to try to accelerate conversion.