I’ve found I have to restrain my initial reaction to my downtrending Dex numbers. It’s especially concerning when, like in your case, it occurs with significant insulin on board following a meal. Like you observed, the Dex can switch from a down-trending arrow to a sideways arrow relatively quickly while it keeps the same BG number. If you had your fingerstick meter with you then you could have verified the actual BG and treated accordingly.
Without additional fingerstick data, I’ve often over-reacted to the Dex’s downtrend warning and over-treated and get an unneeded bounce to the upside. I usually walk without my meter and try to treat trending lows with small carb doses spaced out over time. I like Tic-Tac mints since they only contain about 1 carb for two pieces. I also try to walk after a meal when the Dex trend is moving up. I like to watch the Dex level out and start to trend slowly down and back in my preferred range.
We’ve all been caught out without back-up sugar. I place a high level of importance on always having a source of glucose with me, even if my BG is high and I’m trying to knock down with a walk. Better to have it and not need it than the other way around.
If you’re meeting your BG goals (90-140 or 80-130) a high percentage of time, you’re doing a great job. I don’t think that there’s any specific number of carb grams that’s ideal for everybody when your’e talking about 60 grams per day or so. You know what’s working for you. My only suggestion is to continue to watch your BGs, both fingerstick and Dex, and learn what your body is telling you. You are in a good range; keep it up.