Abdomen Abs - How strengthen above/upper waist without working below waist too much?

I've been doing Fitness Blender on and off for close to two years and I love it. I've never been in better shape, overall, and I can't say enough good things about Fitness Blender. The problem I'm having is my lower abs, the belly part, I can feel how hard the muscles are underneath. I try to keep my belly tucked in while I'm doing the abdominal exercises but it protrudes. In case it helps, I'm considered petite--5'2" with a small frame/bones. And I just turned fifty in autumn of last year. One of the main reasons I started working out was to strengthen muscles, especially my arms and upper body, to help hold my bones up. But I also want to have a nice look, obviously. :) For now, my question is, how can I strengthen and develop my upper abdomen without making my belly muscles protrude too much? For most people, this probably wouldn't be a problem but as a short, petite person, the belly can appear prominent. Thanks for any help anyone can give!