Deflection damage would be a much more radical change.
As for your second question, my current rule of thumb is double far penetration.
So for the vehicles you listed:
- T-70: 80 from 50
- Luchs: 40 from 20
- Ostwind: 70 from 55
- Centaur: 40 from 30
Only when you're pretty much touching the enemy tank, though.
I'm not against radical changes, I am just thinking in terms of which change would result (in my estimation) in a game I enjoy playing more.
The reason I ask about pen is I'd be curious how lethal some of the fast-firing low-damage vehicles would become to armored heavies. In the case of a vehicle that has a burst of 5+ shots, even if only 1-2 penetrate, it's significant damage against something like an Elefant or ISU-152 (or even KT or IS-2, since they're so slow to move).
According to coh2db/com/stats, elefant has 110 rear armor. The centaur would land 1/3rd of its shots if it got behind it.
I know, I know, "if you got flanked you're already dead and...." but just playing it out in my head.