tarev,
That's interesting. I'm not sure why it seems like my Mother's is doing better in with a lot more room. I think it doubled in size within a few months after she repotted it (I can't explain that). Honestly, with all the rain we've gotten at certain points this year, I didn't think any of the cacti in that container were going to fare well, but the opposite seems to be the case.
Planto