Automatic Litterbox Central

i have one big cat and one very big cat. one is about 11 lbs and almost 2. i had to amputate front leg as a kitten, so he's a little more awkward than most cats in the litter box (other than that you'd never know he is missing his spare). the "baby" is 7 months and 11.5 lbs. i expect him to top out at about 14-16 lbs. he's not fat, he's simply a big cat. large head, huge paws and very long. my concern is this: is the simply clean too small for them? i worry about them having enough room in the potty portion of the box without overspraying.
has anyone encountered this issue?

One of my cats is a tripod as well. He lost a back leg due to an SUV incident and he doesn't seem to have any problems using the box. The last time I checked they list 12lbs as the weight limit for the box. There is a dip in the side of the lip that runs around the box, but it is on the short side, so it isn't as likely that it will be a problem. I seem to recall that someone made a sketch of the dimensions of the box and posted it to the forums here, if you think that would help you figure this out.

I'm still very happy with the units I have (8 months of use), and the amount of neglect they will withstand without doing anything "bad". Worst that happens is I will have to do a little manual scooping and vacuum around the box.

My cat is 17 lbs. He's mostly just a really big cat... but he's a little overweight as well. He's never been overfed in his life... but he's indoor and neutered and very inactive... so there you go. I'd love to go with this box since... unlike the "robot"... is not gigantic, it's reasonably priced, it's simple and best of all... it's available locally. The only other auto-box I can buy locally is the Litter Maid... and I hear nothing but bad things about them.