Bob,I have never hunted blacktails and haven't had elk come in while in one but have hunted out of tree stands since I was a kid and I'm now 60.When we first started hunting out of trees,whitetails rarely looked up.I remember being 6'-8' up and whitetails standing a few yards away and being oblivious.After tree stand hunting caught on,that changed quickly and it was common for deer to look up.About that time,I started hunting a wilderness area that was foot travel only and there hadn't been much treestand hunting.I found that these deer also rarely looked up,just like the ones in my high school days.
The point I'm getting at is,when hanging a treestand,it is a good idea to keep it as low as you can get away with,depending on the terrain and animals you hunt.Too steep a shot angle can make a smaller target and may even make it impossible to get both lungs.And I think it is very possible that your animals may not be trained to look up yet.
When I set up for whitetails,I like a distance of 15 yds and a height of 14'-15',to my platform,hopefully with a tree trunk wide enough to hide my silouette.This isn't a radically steep angle.Not too hard to shoot and a good chance for double lungs.
It is even better when I can find a pine that has limbs around me to break my outline.That makes a big difference.Just make sure that you have trimmed anything(ahead of hunting time)that may interfere with your bow or path of the arrow but don't get rid of all your cover.
Animals where you hunt may tolerate a stand 10-12',especially if you have leafy or evergreen limbs that break your outline.A lower shot angle is a plus.You just have to find that happy medium between shot angle and staying out of the line of vision.
Hoofed animals have horizontal pupils.This means their field of vision is much wider than it is top to bottom.Like one of those wide angle scopes.The treestand takes advantage of that.
I didn't hit on the safety stuff because it was covered so well.It is first in importance.most accidents happen climbing up or down.If you hit an animal,we all know to give it time but also give yourself time to calm down and be 100% alert before starting your descent.
Your plan to practice from the stand is perfect.Learn to bend at the waist on steep shots,to keep your torso oriented to the target just like it would be when shooting on the level.
While you are practicing,you can find any possible squeaks or noise issues and address them.I carry a 25' piece of chord to haul bow and pack up and keep that on me,rather than leaving it at the tree as it will have some of my scent on it.
It's not a bad idea to have a plastic bottle or something to relieve youself in, to keep that off the ground around your stand.Just don't get that mixed up with the lemonade.