I think that I have found a bug in Shield Riposte while on the test server. Shield Riposte is supposed to base its strength on your ranks in shield bash, using either the CMAN or the SHIELD skill. Based on my testing, it actually only uses the CMAN. The SHIELD skill counts as a prereq, but improving the SHIELD skill from ranks 2 to 5 has no effect.
Here's my result on Shield Riposte with 5 ranks CMAN sbash and 2 ranks of SHIELD bash:
Reacting instantly to the blow, you lash out with your black tower shield at the troll fighter!
[Roll result: 163 (open d100: 82) Penalties: 14]
Your attack connects!
A Grimswarm troll fighter is knocked off-balance!
Roughly a bonus of 80 to hit (ignoring penalties). Here's my result with 0 ranks of CMAN sbash and 2 ranks SHIELD bash:
Reacting instantly to the blow, you lash out with your black tower shield at the troll ranger!
[Roll result: 90 (open d100: 62) Penalties: 14]
Your attack connects!
The troll ranger manages to keep his footing!
Roughly a bonus of 28 to hit. It does vary a few points by target:
Reacting instantly to the blow, you lash out with your black tower shield at the troll fighter!
[Roll result: 88 (open d100: 52) Penalties: 14]
Your attack connects!
The troll fighter manages to keep her footing!
Roughly a bonus of 36 to hit.
Here's my result with 0 ranks of CMAN sbash and 5 ranks of SHIELD bash:
Reacting instantly to the blow, you lash out with your black tower shield at the troll warrior!
[Roll result: 52 (open d100: 23) Penalties: 17]
Your attack connects!
The troll warrior manages to keep his footing!
Again, roughly a bonus of 28 to hit. Penalties went up 3 points because I was encumbered, so let's call it a bonus of 31 to hit (that keeps the penalty the same).
Basically, Shield Riposte is HUGELY improved by ranks of CMAN sbash but ranks of SHIELD bash have no effect beyond the 2 minimum required to trigger it. That's not consistent with the in-game documentation.