Welcome to HCM
I am glad that your father is taking care of diet and taking antidiabetic
To avoid high post prandial blood sugar he should take food stuff with low glycemic index
and take some physical activity like walking daily. as his fasting blodd sugar is adequately controlled and even pp blood sugar level is resonably controlled but still you can discuss with your endocrinologist
,if he advises some drugs of a group called (AGI) may be added.
to know control of diabetes
in last 3 months a test of glycosylated Hb may be done to know diabetic control.