Hi. Is everything entered on your spreadsheet? I am not seeing many test results, not seeing yo-yoing, so I am thinking maybe you have more info that is not there yet?
You do not want him to have food two hours before his pre-shot test. You want to know the glucose level before you give the shot (and you do not want it impacted/elevated by food). Then, you test, feed and give the shot. When you do mid-cycle tests (4-6 hours after shot), you do not have to worry about taking up food if you leave food out for grazing. If you do not take a pre-shot test, you have no reference point for the mid-cycle test. For example, the last result on your spreadsheet right now is +4 after yesterday evenings shot; it was 340 but you have no idea what the number was before the shot, so you do not know how much it went down due to the shot. It looks like you just changed dose. I know that with Mia, anytime there is a dose change that causes her to hit a lower number than her body has seen in a long time, her body seems to react and we see a few higher than normal numbers. It takes a few days for things to level out.
Stress definitely impacts the numbers. I think that is more true if you have a 'skiddish' cat. Mia falls in that category; she is scared of thunderstorms or any loud and/or unusual sounds. Things like vomiting can even affect their results a bit. Anything that causes stress, exertion or excitement. The impact usually is not that great though and with enough testing data, you begin to learn when those things are playing a role. The Purina DM you are feeding him would definitely impact the results. If I am not mistaken, that has up to 18% carbs. You may want to consider Young Again Zero Mature if you want/need to keep feeding a dry food.
Just my two cents.

I am sure others with more experience will chime in.