[Closed] Possibly daft dropper post question but I'll ask anyway

When it's down where does it go? Do any of them come out the bottom? What I'm really asking is could I run one in a frame with a seat mast rather than an uninterupted seat tube and not have it come out the bottom and interfere with the shock/swingarm at full compression when the seat is down?
Does that make sense? Is it a daft question?
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I have a cheap Forca mechanical one and it kind of telescopes down inside itself but I have no idea if the posh hydraulic ones do this too, I would guess so but bet to check!