My .35 will average about 2" as well at 100 yards with iron sights........I don't shoot it much at this range as my hunting situation doens't allow me to see that far.......so I practice mostly between 50 and 75 yards.
I can get my .35 better at 100 yards if I shoot it single shot with 1 round loaded in the tube. Again, this is the way I hunt, as there is a small possibility of a second shot, but not much likely hood of a third shot. I carry 3 more rounds each in a seperate pocket, so I don't have to worry as much about loosing all of them.......
I've fired the rife loaded a bunch of different ways, and if I fill the tube completely with 6 rounds and put one in the chamber and start firing the groups open considerably......thinking about it, every time a round is ejected and new one loaded in it's place, it changes the spring tension inside the tube and affects the tube, barrel relationship. If I put one in the chamber and one in the tube, fire a round, eject and then load one in the tube........wait a few minutes for the barrel to cool completely and repeat the process I can get pretty good groups.....I've tried firing with a full tube, ejecting and slipping another round in the tube to keep it full but this doesn't make for the best accuracy in my gun either......I've also tried 5 in the tube........etc. etc.....
Doing things to isolate the tube from the barrel, and loading and shooting the same way every time seems to be where the largest gains in accuracy can be had.......followed by loosening the barrel bands, then relieving the forearm from the barrel and improving the trigger. Good handloads would likely make a difference as well.
Again, I think you can improve your groups, but do you really need to?