Sculpt material refinement

Hello,

I am using adapt_type in Sculpt for refinement of inner material (volume 1) inside other material (volume 2). The mesh size in volume 2 should be 20 m and I want to have mesh size in volume 1 of 1.25 m.
I was able to pass from 20 m -> 10 m, 20 m -> 5 m & 20 m -> 2.5 m (see the attached Figure).


However, I cannot reach 20 m -> 1.25 m, please see my input files.
Is there a limitation for refinement in Sculpt?
Thank you very much for help.