I might be misunderstanding here, sometimes turning words into a mental image eludes me. How are you connecting the carabiner to the harness? Are you using the XOP Holiday harness?
I couldn’t get a carabiner to both connect to the leg and waist strap while being comfortable. If the harness manufacturer doesn’t say that the belay loop is fall rated, I’m not comfortable trusting it for that.
This is standard for a climbing harness. That harness is tested to an ansi spec which is brand new, I'm not as familiar with it as I am with the EN and UIAA norms, but they're going to be virtually identical if not identical. (if someone wants to buy the standard for $66 you can compare to the UIAA standard). There is no standard test for a sit-style tree stand harness so XOP is simply following the certification communication standards for a
climbing harness. That means--TIE in to both the waist and legs separately, and CLIP in to the belay loop only. This is what is shown in the instructions.
This accomplishes 2 things:
1) it prevents loading the gate of a carabiner when it is loaded in three directions (3=waist+legs+load), which is much, much weaker than when it is loaded on the major axis. Belay loops exist purely to provide a full-strength attachment for carabiners.
2) when tying in, it eliminates the belay loop so you are relying on fewer links in the chain. This is made for a climbing rope, which is desinged to take a long free-fall which results in a far higher force than it would likely achieve in a tree stand tether application.
They dont show you how to clip in with a prussik, becasue the instructions are from a climbing harness standard, not for a tree stand harness standard. Understand that the belay loop and tie-in on a harness is designed to hold a 15kn load, becasue that's more than the max your body can withstand before suffering major internal trauma. 15kn is just under 3400lb. A 7mm prussik will also hold roughly 3000lb depending on what it's tied to. But neither a prussik nor a rope grab was ever intended to be a primary safety device--prussiks slip, and most rope grabs are much less strong than a prussik and easily strip the sheath off your tether at pretty modest loads. Worrying about the strength of the belay loop is misplaced worry.
If you are worried about anything, clip that prussik to the BELAY LOOP as it's intended and use it to position yourself on your stand, and then BACK IT UP by either clipping the tether below the prussik to your belay loop, or tying in with the end of the tether through the waist and legs.
I would be interested to see the full instructions for the holiday harness, it does not appear to be available on their website.
Edit: if you look at the videos on youtube featuring this harness they dont provide any instruction per se, but they show the xop guy both clipping in to the belay loop as well as running a combo tether/friction hitch directly thru the belay loop. Bottom line, they are using the belay loop because its a full-strength part of the harness designed specifically for the purpose.
This is the exception. This video has some good advice and does provide some instruction.