For the biceps, make a bigger INNER strip and please make sure you're only using E6000 as you may want to make changes down the road if your arms get skinnier. Then make an outer cover strip that's as close to original size as you can without looking silly. Obviously, if you need a lot more room, you don't want a huge inner strip with an outer strip that is barely covering the seems. If you need a cover strip that's 20mm or whatever instead of 15mm, that's fine. Just keep it in the back and not the front.