Before you start changing configurations due to lack of power, I suggest you try using the best rubber available at your current configuration. Then cut a little shorter in small increments. I don't know if Speardiver rubber is the best in the whole world, but it's the best I've used. I do know it's the only small ID rubber available at this time. I'll have more 16mm in about 2 weeks, and also new 14mm in small ID.
Just made some bands with Cressi brown rubber and the ID is 1,8mm.