He means verticle height. How high can your plants possible grow in your setup?
Well, the ceiling is 10 feet tall so I guess they could still grow for a while but I have to keep in mind that I have 25 of them .... The taller they get, the wider they get as well and that could be a problem ... I think!

I donā??t know if anyone can even answer without seeing the setup in person ????

The question is How tall should my 25 plants (under a 1000 HPS) be before I turn over to a 12/12 light cycle in order to maximize yield in a 5 X 5 space with a 10 feet ceiling ???