Dear Matthew
Sorry for the late answer
In deed if you have highly asymmetric peak towards higher angles (probably the 00l family) you could try to characterize the hk0 peaks and at least get an information about the diameters there.
The asymmetry could indicate that you have very few unit cells in the c directions in your domains or some kind of stacking disorder.
With WPPM you will not be able to simulate such asymmetry effects.
You could try debye simulation e.g. with the debyer software (
http://debyer.readthedocs.io/en/latest/) an try to match the observed effect. But the only debye software i am aware of allowing also to approximate the instrument contribution is "Debye"
http://struktur.kemi.dtu.dk/kenny/powder_programs.html .
Not sure about the stacking topic, you may try diffax simulations there...
Regards
Dominique