Reading the OP posts,I would say that the mini Bolbitis in the photo is not b."difformis". It might be a smaller clone of B.heudelotii..but that can't be B.difformis.
Maybe I shouldn't say B.difformis being sold wont grow..but it's got to defeat a high percentage of people who buy them!
One small tip FWIW..my only growing B.difformis is growing near the outlet of my pump. Maybe on non Co2 tanks..water flowing strongly over it helps the plant breath. Not in stone though..
PS.That page in Chinese when translated by google says that B.difformis is native to South America-its not. BUT! It also mentions this plant likes acid water,soft water and a strong flow. There IS some wisdom in those characters.