Foxing bullets need to have explosive terminal performance to ensure an instant kill on a relatively small target, hence why people almost exclusively use Vmax, Blitzking or the like. To get the most out of this type of projectile it needs to be driven fast, very fast, and that means around the 50-55 grain. That weight, bullet type and MV are what dictate the twist rate, hence almost all of the manufacturers have gone with 1:14 and coincidentally is what works best with their offerings in ammunition.
If you are looking for a fast twist to handle heavy for calibre bullets, then you are limiting yourself to bullet designs that aren’t necessarily best suited to what you want them for.
I’m not sure why you would want to run a heavy bullet for foxes, most are taken inside 100yds and I would think that very few are taken beyond 250yds, with a 50 or 55 grain bullet zeroed at 200yds, you are just aiming dead on all the way from zero to 250 yds, and any gain in BC from a heavy bullet over that distance is more than negated by the less than flat trajectory.