Unless necessary to avoid heel strike, moving the weight back is absolutely not preferable. In fact, moving the center of mass of your panniers behind the center of the rear hub is dangerous. If you must do it to avoid heel strike (which likely means you're not riding a touring bike), then it is important to have front panniers for balance.
.... you want to be able to mount the pannier toward the back of the rack.Assuming heel strike is not an issue, why is it preferable to mount panniers toward BACK of the rack?
OP is riding a 60 cm LHT, which is the second largest size. From this I extrapolate that the rider is not particularly short. It is probable, but not guaranteed, that a person who rides a 60 cm frame, has longer than average shoes.
The LHT geometry has the same length chain stay regardless of size. Hence there is the very real possibility of heel strike, depending on the actual shoe size and the specific choice of pannier. Whether you consider the LHT a touring bike is up to you, but the OP has the bike, and isn't likely to be replacing the bike because of a response to a question about rack compatibility. (Most would consider the LHT a fine touring bike).
Moving the pannier back as far as possible does not necessarily mean moving the centre of mass of the load to behind the axle. There remains the mass of anything on the rack, and the possibility of putting denser cargo toward the front of the pannier.
More importantly, when I indicated that you want to be able to move the pannier back on the rack this was as opposed to forward, when your first choice might be blocked by interference between non-adjustable hooks and struts on the rack. There may be a range of positions without heel strike, but some of that range is likely to be taken up with interference. You want to be sure not all of the range is.