Sitting to shoot will seem uncomfortable at first,but once you've done it a few time's it become's second nature.
If you want to shoot both disapline's FT/ Hft ,try UK sarc on your none FT day's.
I think they have an open class that allow's shooter's to sit and shoot,with target's out to 45 yds.
I do not know much about Hft range finding,but i do know that kill size is a clue as to distance on some target's.
I'm sure a fully qualified Hft'er will be along shortly to explain.
Which ever you shoot enjoy it,and keep the wit up,most laugh's i've had outside the vegetable patch
Catch up at bisley