If I'm not mistaken when you block you the reflex damage is a normal attack (maybe slightly reduced). Since tanks don't hit for much that why it doesn't deal much.
No, it's not reduced, it is exactly the same damage as if you do a normal hit. I tested it a lot of times : when i get hit and reflect damages, it is exactly yhe same damage as I would have hit it by myself (whether the damage I do is 5, 837 or 1256).
Also, the math aren't that simple with probabilities, let me explain.
Character A has a% breack defense rate and hit character B who has b% block rate.
Let's assume the hit rate is 100%.
So basicaly, character B has b/100 probability of blocking, but character A has a/100 probability of breaking this defense. So finaly, character A have (1-b/100) (not blocked) + (b/100)*(a/100) (blocked but breacked) probability to make a clear hit.
Example with my characters : 40% break def for 50% block.
(1-50/100) + 40*50/10000 = 50/100 + 20/100 = 70/100 so 70% to hit without being reflected. It works the same way with dodge/hit rate.