Ive got a stiffer arb on and its less understeery than a standard one
Well, maybe. FWD cars do do strange things (sometimes) -- Minis are notoriously strange.
But conventional wisdom is that to kill understeer fit a rear ARB or bin the front one. More precisely, it's a question of the ratio between the ARBs.
This seems born out by the experience of folk who've run Centos in competition. You've got to ask (if fitting a thicker front ARB reduces understeer) what grade of toluene the guys in the drawing office at FIAT were sniffing when they decided to homologate a rear ARB. Did they really want to increase understeer?