Shaman Dancing Axes

[Galirand]

I've started using shamans to heal my black and red dragons, and I've noticed that the description for Dancing Axes doesn't seem to be correct. The descriptions says "the Shaman converts 80% of the inflicted damage into curative energy, healing his own troops"

In one fight the axes did 951 damage and healed both my red and black dragons for 191, in an other fight the axes did 1000 damage and healed for 267.

Does anyone know how the healing done by dancing axes? It seems to be closer to 20% than 80% but in the 2nd case it healing for 26,7% of damage done so there must be more to it.

Ideas anyone?