I tossed 2 grenades at this guy.

End screen said:

40 damage deflected 26 damage to health

40 / (40 + 26)

= 60.6%

The best shield in the game deflects 52.5%

How can this happen?

(Side note: while not conclusive, the guy killed me 100-0 with a Stitcher I so there's a chance he might've even been a free kit with a light shield)