In my opinion, the special ability doesn't work during a city siege. I can't vouch for NHF, but in another mod where I played with it, there was such a bug.
*For example, the "crippling wound" effect is almost incompatible with most other attack effects. And, for example, poison + crippling wound causes the game to crash.
A similar issue has emerged with the "Reinforcements" ability and "Strike from the Heavens." The game seems to simply crash at the stage of "how do I process this."
And, by the way, it turns out that "Strike from the Heavens" is a bug that has been present since the original game, which was simply impossible to detect under normal circumstances!
Added 6 minutes later
I checked the sieges. No, everything works. The only thing is that the catapult still goes first, immediately after the hero (it seems to have a similar mechanic to Krag and Timoha, i.e., it goes out of turn). And the units that are "poured in" can move up to the towers.
*By the way, if you encounter this special ability and Krag's "Breaker" ability, Timoha will do his thing first (attack or pour in stacks), and then Krag will get his turn and perform his "attack" out of turn.
