Do not try to make the Document window 90x90 because you can't ... and ... don't need to anyway.

The Document window can be any size you want ... e.g. 120x120, 200x200, 256x256, 500x500, 523x523 or anything else ...  and Poser will resize it to make a 90x90 thumbnail.

If the window is not square, Poser may clip the thumbnail image that gets shown in the Library.

Try it, you'll like it ... try different sizes and see what happens.

cheers,
dr geep
;=]

Remember ... "With Poser, all things are possible, and poseable!"

cheers,

dr geep ... :o]

edited 10/5/2019