The reason is that in off hand you are trying to time the figure 8 motion.
With a little extra weight it can subdue that figure 8. But the weight of each can is different and can have a different impact. But typically the can adds weight to the front and moves the center of ballance forward.
One of the best drills for increasing stability is to add a couple of pounds to the front barrel. Practice aiming and dry fire with that weight on the end, if you do it the day of or before you have a shoot you will notice that you are a lot more stable.
Typically speaking, and this varies by suppressor.
But typically, a shorter, thicker barrel will have less POI shift. Anything that has LESS barrel whip on firing.
Two barrels at 24"...one a sporter, one a heavy varmint...it's typical for the heavy contour to have less POI shift.
Two barrels with a heavy varmint contour...one at 26 and the other at 20...it's typical for the shorter to have less POI shift.
That shift isn't a big deal for most shooters, because there are very few reasons to ever shoot UNsuppressed ever again, once you have one.