Birds are known for their strength within their bones compared with their lightweight. This is because of their structure (mostly having air pockets) and other factors. Monks can adapt to the same thing with a link to their particular form of training. Other classes do not have the same option because their distinct class limitations are philosophically geared toward different associations to combat than the Monk. Their PT will result directly in Redux but if the Monk chooses a path to go with their PT, they may develop harder bones which give a natural resistance to critical damage as well as a light addition to crit rank (I'd say like decent crit padding up to somewhat crit weighting, to be conservative).

How to get this plugged in to the system would be considerable with the possibility activation by Lore. If they know enough of Transformation then they can activate the PT to be applied with a .X percentage to their crits.