Hard to tell as this is all a dry fit, off the car.
I had to rubber mallet them on. Both sides. Seriously tight.
The pistons are fully depressed and sitting flush with the seals, no doubt.
The pads are as far back as possible. The callipers are not connected to the brake line so nothing is pressurised.
The calliper needs to be forced onto the disc, and then forced off again. It's too tight.
Both sides share the same symptom.
After some research, there are a few different pad widths available. Ranging from 16mm to 17mm.
My Brembo pads, part number: P 06 041 are 17mm.
I know someone with a bench sander and I'll head over there to shave a trifle off the pads for an experiment.
Either way, thinner pads will solve my issue and something to note for others doing this uprade.