bigger rear disc in rear than front a problem I assume?

depends on caliper and swept area as well

if they are tiny 1 pot calipers on the back that use only the middle 66% of the rotor swept area i see less of a problem

brake bias installed set it so the back are almost turned off
do some brake tests on a private road
stop adding in rear brake when all 4 skid at the same time
and then take a smidge out so you still have some balance when its wet

but yeah i agree with poster above you need the fronts to lock first not the rears..