With the AT2 meter you can shoot any BG of 68 or more when dosing according to Tight regulation protocol and 90 using the SLGS method however, getting to the point of shooting that low n either case is done in steps. Have you decided which dosing method you are going to use? If so, can you please add it to your signature when you have a moment so we know when offering advice in the future?
You shot a 173 on Nov 1 but I also notice Cherokee has had some very low readings (under 68) and you didn't take the earned reductions for either dosing method. I am glad to see the dose now reduced to 0.5u as 1u was dropping BG too low but it's possible that dose may still be more than Cherokee needs.
As Nan pointed out, anytime you get a low pre-shot number, stalling (no food) and retesting is the best idea to see if BG is rising on its own.
If you can monitor through the cycle, I think you could set your no shoot level at 170 for now until you see how the 0.5u dose is working for Cherokee and gradually lower that no shoot number from there.
ETA TR info does not apply to the period when ProZinc was being used.