Glad you got it sorted (can't tell you how many times I've posted here and then found the answer myself a bit later).
Note that when you DO match up the T-pose you also ought to go into the property tab (which is located right underneath the "Save" button when you are in the skeleton t-pose fitting) and make sure the spacing and height buttons are checked on to "Auto" (you have to have the tpose set to active for this to work).
Also, you *might* want to go in and set some of the bones yourself. I went ahead and created my own characterization profile so I'd have every single bone (all the spine bones) accounted for. I don't know if the Motion Builder Rig does that (never tried selecting it).
Alienware Aurora R12, Win 10, i9-119000KF, 3.5GHz CPU, 128GB RAM, RTX 3090 (24GB), Samsung 960 Pro 4TB M-2 SSD, TB+ Disk space
Mike "ex-genius" Kelley