Some cats are just bad aimers. We put a box in the bathroom last spring when our arthritic 15 year old Scamperdoo started making puddles in my dirty laundry. I caught on that going through the cat flap and down the big steps into the garage had become too much for her. It's cold out there too, so it probably made her ache like crazy. Since then, all three cats use the box in the bathroom. I saw my hubby's 17 year old Lee-Roy squat with his penis just outside the box and go. I yelled "IN the box Lee-Roy! IN the box!" He stopped and ran. The enormous puddles he left stopped happening but we're still getting little ones. That tells me the girls are having the same problem. It happens when the box is freshly washed and clean, when it's slightly used and when it needs scooping.
After the third morning in a row of cleaning up pee first thing when I get up, I'm thinking of finding the enclosed box out in the garage to see if it stops the problem. Grrr.