Hmmm I play predominantly in full keyboard mode and I would just like to add that I have no issues with the TC unit at all.

Harmonies are all as they should be.

You did know that you can set a keyrange on the TC unit so that it ignores all notes above/below a certain point? (page 21 of the manual).

This split point can be different to the one you use on the keyboard.

I have no split point setup at all on my keyboard only on the harmony m so that it ignores that part of the keyboard I don't want to send to it.
Unless I want a bass sound on the left to play a manual bass, and even then that split only allows 2 octaves for the bass, which is plenty in my experience.
In this case the split point can be the same on both..

Dennis