M620Sie doesn't have adjustable suspension so the front tends to go light. Also the shape of the pillion seat is a tapered towarsd the back so it's not very comfortable.
If it was something you were going to do on a regular basis, I'd think about looking for a Sargent or Corbin seat. I know Sargent do them, and they tend to be more designed for functionality. Also either uprate the suspension to have adjustable compression damping or buy a model that has that already.
That's my 4 penneth worth!