how low are you going after a correction? are you checking at 2 and 4 hours? If you have a sensitivity of 48, and you are getting “one unit too many” kinda says you are at least 96 points off your high target when you correct. Tuning works a lot better for me when I am, say 25-50 points higher than I want when I correct - and then I check to see how far down I go after the correction.
The reason you are getting nuts on the calculation is because it would be easier to imagine if you said “I always get twice as much insulin” then you would just double your sensitivity. if you were getting one unit extra it would only be for a one special blood sugar reading, not across the board.
You can cross check your sensitivity by your TDD (total daily dose) of insulin your endo can do a calculation - or you can get the book “Pumping Insulin” and do it yourself. it’s not hard.
It’s very hard to tell if your correction is too high or too low unless your basal rates are really good. That’s the place I look at when I need a tune up. good luck.