I believe they said 4 to 10.
With an a1c goal of 7.
I never understood tho why are diabetics given goals so much higher than normal numbers?
My lab says 5.5 is normal for the a1c. Why are we given such higher numbers when there is already such a risk if complications. It can't always be to avoid hyos as many are not on insulin or hypo causing meds.
I think your own personal struggle to get within range is a pointer to why the limits are wider than for non diabetics. Insulin treatment is not perfect, and not an exact science. The time delay between the injection and the insulin taking full effect makes dosing difficult to predict and not easy to correct if found to be 'out'.
I feel that this is a factor you need to take onboard in your own journey, and it may be that you need to take account of these effects and that it may not be the insulin failing, but maybe a simple timing and dose control issue.
I think you need to concentrate on getting your basal dose correct so that the fast acting insulin can then be adjusted just to handle the meal peaks. I hope other insulin using T2D can offer advice on how to set your basal and bolus dosing. I cannot advise since it is not in my experience, but I really think it should be your priority now.
Either relax your limits or get medical assistance should be a priority, so that once sorted, then you will be able to start to look at controlling as your diet improves. Insulin needs carbs to work. But starving the insulin by stopping carbs will not be successful.