The culprit in vertical inconsistency is usually arrow creep. Even a tiny bit forward will cause POI changes. Do you use a clicker? If so, check to see that you release consistently at the click. have someone spot you and see if your arrow tips are consistently at the same spot at the shot. The part where you mention being tired is a clue to creeping.
Good luck.

 

I do use a clicker (it's a full OR setup with stabilizers and sight), and I think (but I will definitely pay attention to this) I release consistently at the click; I'll have someone observe this. I improved my horizontal grouping a lot by concentrating on a solid anchor and release. I am trying to also make sure my draw-elbow is at the same elevation each time, since I've wondered if I drop it as I get tired. I also know that variation in my bow arm after the shot can cause problems (such as dropping it, etc.).

 

Vertical mistakes are usually something on the front side. Try to pay more attention to you pressure point, and keeping it the same.

 

For me, it is usually this ^^^^

 

Finger pressure percentages on drawing hand may also contribute to a vertical spread. I know that as I get to the end of a long session I have to be more mindful of my grip on the string or my fingers are liable to start doing their own thing.

 

It could be something as simple as tuning your nock height. You may want to play around adjusting your nocking point first up and then down until you find where you have the smallest spread.

 

I would guess hand pressure on the grip or the balance of finger pressure in the bow hand.

Is your sight getting a good float on the target, or do you feel it wanting to drift?

 

My sight can be pretty steady on the target at close range, but once I get out to 50-70m, it floats around a lot. It almost seems as if there is a magnet pulling it down and preventing me from raising it up. I have a fairly high grip, and have wondered if that could be a factor in this. I've played with tiller, and even at 0 the downward drift is still there. I'm going to start paying very close attention to my pressure point, to make sure that is consistent

 

This is most likely a stabilizer issue. Add a little more weight to your side rods or take weight off the long rod. If you have an adjustable v-bar, then you can bring the side rods more parallel with the ground if they are pointed down a bit.

Don't play with your tiller for this, keep the tiller that is most forgiving. Good, a more consistent pressure point will help with vertical grouping and clicker timing.

 

Maybe try focusing on aiming from the waist? It could be that the elevated aim at longer distances is causing you to lift the bow arm or heel the bow in an effort to drive it upwards.

 

^^^^^ this.

 

Thanks for all these helpful suggestions. Yesterday I changed my stab setup (more weight on back, less on front), and also put some putty on a spare grip, to see if that will help me be more consistent in my bow hand. I could only shoot at 10m at home, and this weekend plan to shoot it at longer distances to see if this helps.