mmh no expert, BUT., here goes my take.....

I believe your premise is correct
You do or have increased your tolerance to carbs, short term.
As have I , I suspect.
But given it took me 60 odd years to get to T2D status, I'm pretty sure that Tolerance is short and within months of higher carbs I'd be back at my DX level of HBA1c.
Regarding the morning FBG, perhaps it is similar to checking the car oil level.?
we've been standing all night unused, everything glucose wise has drip, drip, dripped back into place, and levelled out.
Sure you know all this, but just to explain my thinking for others.
That why we take that check before we have had food or exerted ourselves.
because once the day begins just like starting a car the (Oil/Glucose) gets sloshed around as we idle, rev up, or speed off
all of which uses and makes call on the energy source, gas/glucose
That FBG, given the caveman scenario of olden times, is something the body generates, to enable us, if we had gone without food or too little of it, the day previous.
(Our bodies as hosts to us, gets a bit concerned, we MIGHT kill it, so it looks out for us.)
In this case by giving us sufficient energy to HUNT/Scavenge, so we can eat, and thus save our Body from harm.
However in the modern day, for T2D we have the opposite problem, to much to begin with, so any extra not required.
(see Jason Fung for further info. Best book I've read on T2D '
The Diabetes Code)
So i see that FBG rather like measuring something toxic (to us certainly)
bit of a conundrum,
Given we have all blamed the odd FBG on foods etc,
but it's a slow riser over time, as the toxicity within us grows,
so i do believe it is better as a longer term predictor of just where we are on that toxic glucose scale, so more use as an average, rather then a high low water mark on any given day.
Took a few weeks for mine to come down to sensible levels after DX, was bobbing along in the 5-6 zone quite happily, but since my mishap, it rarely ducks below 7..ho hum
Happy to hear others ideas/opinions and being shot down in flames..