mark is that with new pads fitted & fluid pressure ?? just try loosening off the caliper bolts after you bleed them & even after a drive then check the caliper space to strut just get the calipers central to the disc
I just had a quick look at mine and i've spaced them out about 6.5mm, which was the supplied washer plus another standard washer. I did this to put the centre of the caliper inline with the centre plane of the disc. I don't recall having to do this on dad's car (Mk2 struts) bit mine are capri struts/mk2 calipers so there might be a difference because of that.
The washers should be half the additional thickness of the disc, so for (say) a 20.8mm vented disc replacing a 12.7mm solid disc, that would be half of 20.8-12.7 or 4.05mm. I say "should be" because production tolerances will mean you may want to add or subtract a bit in order to center the caliper over the disc exactly, although in practice even that may not matter.