From the relative
commit:
The new formula is:
2/5 * shield_penalty^2 / (20 - 3 * racial_factor) * (27 - shield_skill) / 27
where shield_penalty is 5 for bucklers, 9 for kite shields, and 13 for tower
shields, and racial_factor is -2 for large species and formicids, 0 for
medium species, 2 for kobolds, and 4 for spriggans.
So large species are still favored in shield-use, albeit unfortunately is not so evident in game as before.
I personally don't have idea in the practice the new formula has similar "returns" for larger race, or their "bonus" is weaker than before.
Also please not there at least another relevant
commit that adjust some number for kite and large shield, so again the new version could have a different balance in comparison of the past.
From my very limited experience with normal races, now kite and tower shield are much more usable at lower skills, especially when spell-casting, but they provide lower bonus until getting similar skill level to the past. No idea with UC.