as said there is'nt a load compensator valve on the rear beam on ibiza cupra mk3.... presume yours is mk3. mk2's can have them on model dependant.

ABS does all the proportioning based on ABS pump and ABs sensors themselves. Barring a hydraulic issue which is reducing front brake effort for some reason, then you have no biasing to adjust.

MK2 golfs have compensator and could have this phenonemon but mk3 ibiza has no such device.

Something else dude.