Hi
@SRO, it sounds as though you haven't had a proper explanation of the two insulins.
The basal insulin is used to maintain a background level of insulin that, in the absence of food, ensures that normal processes that metabolise protein into glucose don't cause your blood glucose to rise.
The bolus, as you know, is used to manage the carbohydrate that comes from food.
Basal testing (
https://mysugr.com/basal-rate-testing/) allows you to determine that your insulin is at the right level to maintain a stable blood glucose level in the absence of food.
Once you can confirm this, you will be able to go back to confirming that you have the right level of bolus insulin. This is usually described as an amount that, 2 hours after eating, ensures that your blood glucose hasn't risen more than 2mmol/l from where it was before eating, and returns your glucose to roughly the same level four hours post eating.
The attached document here:
http://www.imperialendo.co.uk/CHO Counting.pdf is very helpful in relation to basic understanding of carb counting, dosage and adjusting insulin, and I strongly recommend reading it. You can also use the
BDEC course to learn a similar set of skills.
The Imperial document will also give you an indication how to work out a correction dose allowing you to bring that 16 to 12.