VW Polo 9N3 1.9TDI AXR
brake system FA: 256mm ATE54 FS-III
brake system RA: 232mm Lucas C34
control unit: 6Q0 907 379 AQ
Component: ESP 8.0 front H04 0002
Coding: 0002371

another possibility is that the Polo diesel uses smaller 34mm rear caliper pistons compared to Gti 38mm ones. Thats 20% smaller. If an MC swap for whatever reason proves impossible then perhaps a combination of the stock rear disc with the diesels calipers might produce a better pedal, but at the expense of rear braking power?