Four months?!! whew......
I'll worry less myself then. I'm as stumped as you are rockclimber. The little potty I bought worked from day one! Till I ran out of the stuff to put in it? which someone said here may actually be scented to attract hammies to it as an outhouse. Worked for me.
Since then nothing has worked in providing a consistent toilet corner so far as I can tell. Constant spot checks show not a single place is being used apart from anywhere else. Thick substrate may account for it. Waiting till payday to find the pellets for the potty to see what happens then. Yup, I've tried moving soiled bedding to one place etc.....its all a mystery so far. The plus in my situation is he doesn't do it in his food, but he has three nests or so in this weather....not there either....
When he lets it rip in the wheel I think he's just happy....
or excited.....
I spose it's possible that not ALL hams will have one spot? even if they did once? and I feel better knowing four months can go by without singling out a spot as well.....trial and error. I always try to keep in mind how OCD they are about their living space when making changes or interfering in their cage...and will probably encounter something insignificant to me that drives the hammy bonkers.