You can buy a wider English breastcollar that instead of going into the rings, slips over the girth on both sides just below the buckles. My trainer uses one on her big Hanoverian because he's just so BIG. Gracie is tall but quite narrow, and the narrow high breastplate with the rings works just fine on her. The elastic ones that hook into the rings tend to ride too high on her and cut into her windpipe - I don't like them on her at all.
This is the kind of breastplate my trainer uses:
But this one is elastic, hers is all leather. I think the elastic looks a little tacky and like the plain leather. It's about the same width, has the same little keeper strap over the neck. She hunts all day in it with no slippage or problems with fit, and Dante is one BIG horse.
See... Attaching it to the girth leathers works in a flat saddle like that, but not in mine... In mine, it has to come over the knee rolls and it just isn't good. If that would work, I'd use the same elastic one I have, but it sits really awkward.