Welcome to the forum
@Vikingwarrior
Congratulations on your impressive exercise routine. How do you manage your diabetes generally? Is it with pens or an insulin pump?
The first thing to say is that almost certainly all of your friend and family would say that you have a completely flat stomach and they don't know how you do it. We tend to be far more critical of our own appearance than others are, and particularly where we have one thing that bugs us, we artificially amplify it. Try to see yourself through others' eyes.
The second thing is that this is a bit of cultural weirdness. A completely flat stomach isn't actually natural. It's supposed to swell out a little. So it may be that your current level of flat-ness is much closer to an ideal natural bodyshape than you are thinking.
Having said all that, I was thinking about my stomach the other day as it's showing a little more of a 'relaxed' appearance as it often does at this point in the winter and after the treats and extra feeding at Christmas.
When I was on MDI I was a bit lazy with injection rotation and while I tried to use different areas it was so much easier to use my abdomen that I defaulted there (because it was so easy to just lift up my shirt wherever I was and gain access) and just 'moved injections around a bit' more often than I perhaps should have, particularly on my left side as I'm left handed. As a result, over the decades I did see a little bit of fat gain under the skin in that location (so this is an area I've tried to target before).
I'm still more or less the same weight I was then diagnosed 30-odd years ago, but just that one area shows evidence of a smidge of 'lipohypertrophy'. So if you are using your stomach and abdomen for injection or infusion and have been for a while, it might be a good idea to shift and rotate your sites to pastures new.
I also think it's a good idea to consult with trainers at your gym (or even do a bit of YouTubing) for a wider variety of abdominal exercises to ensure you are tightening all the muscles in that area. Crunches are good, but you also want to target lower abs with leg lifts, and ensure you are doing both straight and diagonal crunches. Something like planking to exercise the whole core is almost certainly also worthwhile.
You might also find that you get a significant difference by working on posture. There are simple pilates routines that don't feel like you are doing much, but really help you to stand better, and hey-presto bits of you that used to slump or stick out are suddenly pulled into line.
Hope that gives you some ideas. Generally when I decide I need to do a little maintenance, I can make some changes, but some of the lipo swelling always remains, and possibly always will unless I did some drastic starvation/dehydration type thing that movie stars mention when training for a role, and frankly I'm not going there
