Yup, there's about 1-1/16" from the frame to the inside of the spring, no arguing that. 9/16" of that is space, the other 1/2" is bracket and bushing. Pretty obvious in the picture.
Since the bracket and bushing can't go inside of the frame rail, the bracket can only move over 9/16". Since the bracket doesn't even sit flush with the frame, you only get about a 1/2". So how far can the spring move at the bracket? About a 1/2". No more, unless you somehow move the bracket inside the frame rail.
So, can you move the perch 3/4"? Sure. Does that move the spring 3/4"? Only at the perch. At the bracket, the spring is still only offset a 1/2". So, how much tire space does that get you? Well, let's see- something less than 3/4" and maybe a little more than 1/2". Since the spot that the tires rub on the spring is closer to the bracket than the perch, you get a smidge more than a 1/2", and you put a bind on the spring for your trouble. A 1/4" isn't much to squeeze the springs, but it won't even get you an extra 1/8" of actual tire clearance, so why do it?
Even with the springs offset a 1/2", the springs aren't the tire clearance issue. If you don't move the inside of the wheel tub, the 1/2" offset is all you can actually use anyway, because that puts the outside of the spring even with, or slightly inside, the wheel tub opening. So, even if you only move the perches a 1/2" to keep them inline with the brackets, you end up rubbing on the wheel tub before the springs anyway. The 295's on my Duster have never touched the springs, but they do occasionally kiss the inside of the wheel tub if I hit a driveway drainage or dip too fast.
