Advice on best place to fit air vent on viv?

[Bigpapapowell]

4'x18"x18" viv housing a royal,
currently with no air vent apart from the small mesh square where the ceramic heater sits on,

Would it be better to have the vent on the hot end or cool end? or both?

[Joshh]

i have one going across the whole of the back of the viv and for my leo it has just on in the middle