When I say seat position man I mean exactly that- handling.
Single heaviest object in the kart is the driver, about half the weight.
Shift that weight one or two inches backwards or forwards and you can set the handling characteristics right there.
If you were in a “long” kart and didn’t use the pad to bring you up close- sure as $hit it’s gonna understeer since F/R distribution leans more heavily towards the rears.