Our home has only 4 return air vents and 1 is in a very small bedroom. We are trying to determine how close furniture can be to the return air vent near the floor and not block it. For example, the beds we have are considered captain's bed and have an mattress on a thin platform that overhand the base of drawers by about 3" all the way around. That would leave a space of 3" from the floor to approx. 13" up for air to flow. Is this enough space? The bed has drawers under it and is not open. Would it be better to remove a drawer which would basically extend the vent the width of the twin mattress.

Any thoughts would be greatly appreciated. Thank you.