Vet suggested +6, so that is why I always tested at +6.
Cat's don't always have their lowest numbers at +6, even though this might be roughly where you are getting peak insulin action. Until a cat is well regulated when they have their nadir (lowest number) can be anywhere in the cycle. Before George became well regulated he nadired as early as +2 and as late as +13

though he was more usually in the the +5/+6 mark for his nadir.
I would encourage you to spot check at other times, it can help build a cleared picture, and can help you manage his cycles and dosing more easily.
With his amps being lower than that +6 last night, I'm wondering whether his BG is acutually dropping into preshot (or even flat), it may indicate an active cycle, for George it was usually a signal for me, so I would be sure to get a +2 so I could manage his numbers if need be.
ECID, judging when they drop and how far they are likely to drop by, will come by gathering the appropriate data.
Though this dose, on the surface, does appear to not be getting him into nice numbers, for me, there are a few to many unknowns to suggest an increase just yet. On june 7th he dropped by almost 200pts (could have been clearing a bounce, that can lead to lower numbers), but there are no test after +6 that day nor indeed a pmps or tests that evening, with the way he shot up by June 8th, I wonder if he saw something lower in that pm cycle.
If he did see something lower on June 7th which triggered a bounce that would be due to clear by end of today (bounces can last up to 6 cycles/ sometimes less). So if you are able to get some tests in this morning (earlier in the cycle +3 at the latest) or run a curve perhaps if you have time. The fact that his ps is lower than +6 last night, makes me think that he may be looking to clear a bounce.
If you are able to get those tests in today and you don't see any green/low blue, then perhaps an increase would be indicated.
But please note that with SLGS you would hold the dose for a week,
and run a curve before taking the dose up.
If you want to follow TR, you need to always be getting at least one test in the PM cycle, always testing before giving the shot, goes without saying.
Perhaps see what today brings and ask a question about dosing after you have todays numbers in.