I always found that bounces from steep drops brought worse bounce numbers that those from going lower than used to. Eddie really likes to fall of the cliff when he onsets, which is why giving him some fresh food (carbs) maybe 30 minutes before onset might help slow that plunge.
When you say "onset" do you mean nadir? Also, it's not always going to be possible to give him food (do you mean LC or MC) 30 minutes before if I'm not at home!
The second thing that could be at play is lack of duration. If you give him food after nadir, you can shorten duration, thus causing higher numbers for the following preshot. Which in turns means an even deeper dive at the following onset. More bounce, lather, rinse, repeat.
Ok, well, I feed him, as we've discussed 4 times daily (more if he goes plunging, of course) and it looks like this:
AMPS
Breakfast & insulin
+3 small lunch
+8 small portion (not dinner)
PMPS
Dinner + insulin
PMPS +2: a LC snack.
As for petsitter dose, you might want to try it a couple days before you go, so you can see what he does on that dose. If, for example, you took a little off to 7.5 units, it's on the line and easier for the petsitter to draw. If you start it tomorrow, you could see what he does on that dose before you go and see if it'll work for the few days, or he needs to go down further while you are gone.