Well it’s not what I thought it was as it only happens when setting the added body to the Root Bone in PHAT and setting it to Kinematic. Simulate works fine and doesn’t send the character into the air but the blending doesn’t work… ahhhh… 
Hello ,
Unfortunately I wasn’t able to find out much about another solution in the time that I was looking into this. The entire thing isn’t something that I am familiar with in the first place. It seems like you are making progress however. If you do find out any definitive solution, please be sure to post it here as it would be great to know.