Our whitetails are not large. I"ve killed over 100 head of big game, hogs and deer mostly, wiht my bow. So take this for what its worth.
I've seen more than a few frontal shots and if hit just right, its gravy... but its a small target. On an animal that almost always moves before the arrow gets there.
Add in the fact that the ribs are staggered like fish scales and form a shield from the front, mother natures way of providing protection, if the hit isn't perfect, then it often slides under the skin but not into the vitals at all.
The opposite from this is that the angled away from you shot, the ribs are stacked to catch an arrow and basically help or force it to penetrate. Thats a nice one to take IMHO.
FWIW I'd never ever shoot a facing on deer ever again with an arrow. If you nail the heart, fine. But err a bit and get only one lung or part of a liver etc.... its going to be slow going and one lung won't always kill a deer.
I'd imagine simply that an elk, had I any experience on them, would be only tougher than a deer. Of course it may be true that elk don't move at the shot like a deer does. And if thats the case, then at close range, it should be a fairly easy target to hit. But video I"ve seen from elk, also tells me they move more than you'd think..... Hitting a canteloupe at 20 yards.. no problem. Not having time to figure if its 20 or 25 or 15 yards..... and the idea that at the release the animal will move some, but who knows how much or which way.... nah, not on an animal for me. Elk or otherwise.
NO would be the answer I'd give from my whitetail experiences.
