Kitten not squatting down to pee in Litter Box

Hi! I'm new here & was wondering if anyone could give me some advice.

We have two male kittens Cosmo & Oscar (both neutered) who are 5 months old. Recently one has taken to standing up in the litter box when peeing. This means the pee is mainly going on the floor not in the litter box.

Any idea why he is doing this?

We were thinking of getting a cat toilet to solve the problem. Is this a good idea or not?

Any advice would be appreciated

One of my males urinates standing up, so to avoid problems we made our own litter boxes out of large Rubbermaid storage bins by cutting a door in the side and leaving the lid off for better ventilation. The sides are so high they cannot urinate over the edge, which also works well for cat or kittens that tend to throw a lot of litter out of the box. If you decide to go this route I would definitely recommend finding a storage container with a flat bottom (many dip down at the edges and gather too much urine) to make scooping much easier. Hope that helps some.