I tend to run a bit more rear brakes so prefer the adjustability of a bios valve, so perhaps by changing your pressure reducers for an adjustable bios valve it may balance the car a bit more. Perhaps your reducers are sending very little pressure to the rear.
As for the way you have the m/c piped, I cant see it being any different to have it being crossed over. The front 2 ports are linked, the rear 2 ports are linked. Having the fronts piped from one side, and rears from the other wont matter.
I am assuming that your brakes are currently working well and not pulling to either side when you jump on them, just locking the fronts.
If its just one front, then look at bleeding them and/or checking caliper condition.
If its both, then get stickier tyres!