My penultimate booth had rear filter. Current design uses the slanted back and up, mostly back. I don't like the bottom filter. Seems to me it encourages pulling spray hanging in the air to settle on model. Upward would be nice, but I like a light in roof of booth, but I think a filter on top would not leave much room for light.
The position of the filter is what is critical, since air is drawn towards the filter. My penultimate booth had filter on the back, followed by plenum to side fan. Many bottom filter booths have fans in various places.