I am three years (almost) from diagnosis, can eat more carbs without seeing high BG levels - but it immediately increases my weight.
To eat more carbs on a daily basis and not see a rise in Hba1c would be rather strange, because it would most likely be working back to fully fledged diabetes.
I wonder if you are clinging to the Metformin in the hope it does the job, rather than relying on low carb eating to tame the problem with glucose.
It might have been lucky that I could not take Metformin as I find no temptation from carbs, as the thought of being pressured to take tablets which tried to turn me inside out is more than enough to strengthen my willpower.