From what you say you definitely don't have auto preload adjustment, so please ignore what I said before!
I can see how you may find the bike rides a bit too high on the rider + pillion setting as your wife is fairly light, so may not meet BMW's average pillion weight assumption. That's the problem with the old system, the three settings are based on BMW's idea of what the average rider, pillion and luggage weights are, so the amount of preload applied is not going to be exactly right in many cases. This is where the new system is an improvement because it effectively measures the load on the bike and sets the preload to exactly the right amount for that actual load, and also uses this information to fine tune the damping for the load too.
Unfortunately with the new system they have taken away one of the damping options leaving soft and hard neither of which seem to work very well.