Rules R03 and G23 specify the projected cylinder is horizontal,
with a very clear picture of a robot enclosed in a figurative cylinder with its bottom base mashed against the ground and the top face parallel with the roof of the arena.
For future reference, FRC doesn't like it when you lawyer the rules, so I would avoid it. The spirit of the rule is made very clear with both the diagram and repetition of the rule.
Good Luck!