I know my friend who loaned me this 1202 hatched eggs on the bottom/floor of the incubator, but she's out of town right now so I can't ask her how those hatched. Seems to me the bator would be awfully crowded in the bottom if all three trays plus the bottom hatched...because I know my chicks jumped down to the bottom.
I also know they sell the separate hatching trays, so I guess you could replace the three trays with those so they don't jump out, leaving the guys on the floor with plenty of room. You'd like have to use cartons or egg racks though, so they keep air flow around them.