Here is Dr. Lisa's page on
How Much to Feed. ECID, and GuMung is younger so probably a bit more active than some of the older cats here. Do you have an optimal weight from your vet for GuMung? Assuming it's 14lb (though that's a bit large), then Dr. Pierson's formula to give you a general idea is which for GuMung would work out to about 257 calories. Or a little over 2 cans of that Wellness per day. Don't forget to add the calories from any pokie treats. Note, Neko was around 14.5lb (Maine Coon plus acro) and she needed around 200-220 calories a day to maintain. I used the scale to determine what calories worked to keep her where I wanted her. Again, ECID.
That +6.5 could also be the insulin finally starting to wear off.