I was wondering how much light I would lose by having a 400hps roughly 3ft from two plants without any reflective material in a 3'x5'x5.5'(depth, length, height). I don't use the whole area just a portion
What you need is one of them thar light distance charts, like this one that I just found for you in the Lighting forum: My flowering space had beige walls. Few growers understand the power of beige! Though, to be honest, I did finally just get around to painting it flat white.
Just paint the inside of whatever you are using white. It reflects great. It also depends if you keep your lights cooled as then you can move them closer.
How much light you would lose compared to what? Are you asking about the distance of the light or about reflective materials?
That could only be determined by taking actual measurements in your particular space, there are too many variables at play. I don't see why this has to be an issue -- just paint the walls a flat bright white, or get some cardboard to make reflection walls and paint them. Simple, easy, cheap.