off topic: is it common to have a litter box in a bathroom? According to the things I've read, cats prefer to have their "scent soaker" in more common areas, so I've not ventured there...

I think a lot of people do it so they only have one place that's a bit smelly instead of two

We do. Tiles, not carpeted. Keeps smells away from living room etc.

When living in a larger house, I had the litter box under the stairs, in a small apartment, bathroom was the best option.

Fairly common - if say ~20% of cat owners I know keep the litter box in the bathroom.