Why cant Mr B get the hang of litter training?

Snowdrop still leaves the odd near her tray but is generally very good, Strawbs is perfect with his, never a stray poo.

Mr B is a whole other matter! He uses his tray in his cage but as soon as we let him out he leaves puddles of wee in every corner of the room and poos everywhere!

Will he get it as he gets older like Snow and Strawbs did? When we move he will be free range and I dont want wee everywhere so I need to find a solution!