It shouldn’t be the case.

What kind of curve do you have in the back?
Also, are you doing this on sand paper? If so and if you kept your larger chisel to the end, perhaps you should change your paper.

Final question: are all your chisels of the same making?

That the chisel is 1″ should not make too much difference. True, more metal has to be removed than on a 1/2 inch chisel, but a lot less has to be removed than on a plane iron. And if the back is flat and polished, and the bevel on your chisel is already established (often 25 degrees to 30 degrees — though I never actually measure mine), not much metal has to come off to get the edge for it to be sharp.

Are you sharpening using Paul’s method? When I find I did not get a sharp edge, it is often because I simply did not sharpen all the way to the edge. I often take a quick look at the edge after the coarse stone to make sure the scratches are all the way to the edge and square across (to make sure I am not sharpening out of square). You should also be able to feel a burr, unless the course stone simply broke it off already, which I find happens. In any event, if after the medium stone, you still cannot feel a burr, you did not sharpen all the way to the edge. No burr, no sharp edge. It does not have to be large, but it must be there. That burr gets polished off on finer stones or, on Paul’s method, on the strop.

If you used your stones correctly, there is a second way you might get a poor edge. You might have a great edge and then round it off on the strop. You have to PULL the blade across the strop being careful not to raise the blade us so as to blunt the edge.

You mention a sanding belt. Are you just using that, laying flat on a benchtop or whatever, to flatten the back? Or are you doing some sort of power sharpening with the belt to establish the basic edge before turning to stones? That was not clear from your post.

A low quality photo of a 7/8″ chisel, showing that it is quite thick, with a corresponding long bevel. So, it will require more work to sharpen it compared to a ½” one, which also will have a shorter bevel.

A few “for-whatever-they-are-worth” thoughts on aids on grinding and coarse sharpening.

3M offers sandpapers with adhesive on the back. They stick very nicely to a granite slab (rightmost on photo below) or float glass. In addition to the need of all sandpapers to frequently be cleaned from ground off iron, they are also not inexpensive. Re-mountable photo glue on the back of ordinary sandpaper is a less costly alternative. Clamps can of course also be used. The paper will wear down, but my DMT 120 grit diamond stone did that as well.

Centre of the photo shows a belt sander designed for tool sharpening. Thanks to that the belt speed can be varied, sparks can be avoided, though even so intermittent water cooling is required. It’s quick compared to manual work on sandpaper and thanks to a honing guide the results are no less accurate. It’s a useful machine for shop-made irons. As long as one is prepared to change belts from coarse to very fine, it can replace the Tormek next to it for final sharpening.