Well, too small is subjective. I understand your concerns tho. I have a sidebath 16 footer. It IS small. Because of the curve of the roof, if I was much taller I wouldn't be able to stand upright (I'm 5'7"). But, I expected to need to sit on the throne to shower. Remember, for every inch of space taken up by a bathroom, you're taking that space from somewhere. I'd rather have the space used for areas that I use for other things... like cabinet space. A side bath provides a more open feeling in a 5th wheel and ventilation is better for both heating and cooling ... you're not blocking the loft area. With a front bath you might as well be in a 16 foot front bath trailer... they pretty much look the same inside. The real deal breaker maybe not the size of the bath, but how one has to crawl into the loft. In the side bath 5th wheel there isn't any stairs. You would literally step on the couch and crawl up into the loft on your hands and knees. I know of at least two side bath models that have been modified to provide stairs, so that's very doable. It just depends on your skills or budget.
I know this doesn't answer your questions, hopefully someone will give you the dimensions you seek. If you can view a side bath 16 foot trailer, go look... the bath is the same as the 5th wheel.
If you want the best of both worlds, get an Escape
5th wheel... it has a big side bath!