I can see a bit of mirror distortion being introduced if the lock screws are tooo tight. I wouldn't rely on the thickness of the 'cork' packing to provide the expansion/grip req'd. As Andrew has just mentioned, seems like a bit of redesigning might have helped.
Still, If you do your collimation correctly, it shouldn't change by simply going from 45 deg. to vertical!
The lock screws should never be too tight or used to adjust the collimation.
Use heavier springs or *bottom them out* & then ease each adjuster till you are collimated, then just *NIP* the lock screws.
My 2cents.
L.