So many things to watch our for.....

re diabetes. You can only make one change at a time but what do others usually look out for first ie basal or qa & look at re making changes
1. difference between bedtime & fasting levels
2. keeping an eye on all levels during the day ie from meal to meal

If you're having problems I would make sure basal is correct first, zero or v. low carb day of testing (plus the dreaded overnight/3am tests), BG should hold steady, once this is dialled in you can play with QA and ratios, without that you could be going up or down due to basal and not know.

If its over night then the basal is the first to look at.......

I would always suspect that basal needs adjusting as I would rather adjust it than change my ratios, but theoretically if you have tested your basal recently and you are getting a high reading before the same meal consistently, then the QA is a good bet...

I would focus on the bedtime to fasting level differences if this is causing concern. If your waking sugars are either high or hypo resulting in a rebound high it can take you up to 4 hours during the day to correct from that which adds onto the 7 hours overnight that it also probably wasn't quite right. If you focus just on your meals then that only really alters just 4 hours at a time. My HBA went from 7.4% to 5.9% in 6 months as a result of nailing my overnight - because a large proportion of my "day" (hours in the day) was wrong but didn't stand out on paper as much because most of my daytime scores were happy little averages but because I didn't have the same volume of night time tests on paper I hadn't seen as dominantly where my average was being pulled up by.