Thor FM via mod-busses

[Mich01]

Hi Folks,

At the moment I am exploring FM synthesis with Thor's analog oscillators.
One of the things I try to achieve is creating a saw-like and a pulse-like wave, using two oscillators (ratio) and some feedback. (Just as the way it works in the Yamaha DX synths). I manage the ratio with the oct-knobs on the oscillators. The FM and the feedback I try to create via some mod-busses.
Somehow I do not even come close to a result.
I do get FM modulation, but it's almost not musically adjustable (like DX).

Has this something to do with the difference between exponential/linear FM synthesis?
(In Thor I always thought that modulating pitch stood for exponential, and modulating frequency for linear).

Does anybody has tips?

Thanks and regards
Michel