smoothing during morphing

Hi all,

I would like to morph a long stc file (few minutes) from an individual
brain to an average brain. I have a question concerning smoothing factor
(the --smooth option) and how it interacts with morphgrade (--morphgrade
option). In your experience does a smoothing factor of 5 go with a
morphgrade of 3? I suppose the source grid spacing also plays a role in
this?

Kindly note that my source grid is rather sparse to keep the file size
computationally feasible (15 mm). Any insights are appreciated.

Thanks in advance,
Pavan