My Ham poops/pees in and below her wheel?

[PishPash]

I'm trying to set up a litter-box in my hamster's tank. Most people suggest I find the corner they pee/poop in most and set the litter box there; put some soiled bedding inside, etc.
Well, my hamster was peeing primarily in the front left corner of her tank but after I got her a larger wood wheel she seems to spend a lot of time running in it and poops around its base and the opening. The poops aren't wet or anything. If you think something is wrong though please tell me.
She's in a 20 gallon long tank which I'm planning to change to a bin cage with more room soon, but even so, I doubt she's wanting for space to poop right now.
Should I just go ahead and take a bit of soiled bedding and put it in the litter tray near the wheel? If I move it away from the wheel over the course of several days do you think she'll go in it??
I just wonder because I would much prefer her to be "potty trained" as it would make spot cleaning easier.