Most of the ones that slope toward the front have a MONTE CARLO comb. you see them on trap guns a lot, and on hard recoiling sporting rifles, like the old Weatherby magnums.
But they usually have an area between the rear of the comb and the heel where the comb abruptly drops back down and blends into the heel, allowing for a normal sized buttplate, otherwise the buttplate would be very tall and ungainly.
Is that what you are referring to, or one where the top of the comb is a straight line to the heel?
SRH