Here's what I do with my smoothbores to combat mirage, not that it wouldn't work w/ rifles. But my flint BP rifles are for hunting use, otherwise my flint smoothies get shot 100X more than the 'riffles' do.
For my first few shots from either arm, I'll "imprint" in my mind where the top of the barrel is in relation to the top of the sight blade. Once mirage builds up, my focus will 'shift' to where I'm holding the top of the barrel to where I need to hold it, for the roundball to impact where desired. On woods walks, it'll become 2nd nature where to hold the barrel in relation to the sight height, to still hit the gong or whatever target, where tight degrees of high/low shots are usually not needed.
If the bullseye, for example, was a black bull of 9 & 10 ring, using this method I'll 'hit black' most if not all the time. This technique of 'aiming for black' is also extensively used in modern centerfire high power matches and I only mention that to prove a point.
Now in a match, yes I may score a 8 or a 9, where a rifle (with or without mirage) may be capable of scoring the 10, but ~1-point out ain't bad! It works! As honestly in competition, when I'm 'on' (the nut behind the trigger is working ... ) my smoothie scores are usually right up there w/ the top rifle scores. Try it!
