This may not work in the jumping world, but I'll offer it anyways...
I usually turn my leather strap so the buckle is on the inside, and then adjust it so the buckle is near my stirrup. That way, when my foot is in the stirrup, the buckle is away from my leg, and the buckle is not adding to the bulk at the stirrup bar - it is just two layers of leather folded over the bar. But it looks odd.
If you really
don't mine being different, you could use Aussie leathers. They are designed so the buckle is also low, but it is hidden inside the 2.5" strap. I've used them on English saddles. They work fine, but you would get a lot
of strange looks.
I tried the Bates version of webbers and hated them - they felt flimsy and didn't fit my leg. These have tempted me, but I've been spending so much on training bills that I haven't wanted to shell out more on tack.
Links below: Prestige Ideal Dressage Stirrup Leathers - Quality Tack at Outlet Prices - VTO Saddlery Stubben Webbers - Quality Tack at Outlet Prices - VTO Saddlery
Those look sturdy, and would reduce the bulk at the top.