I don't have a Beseler enlarger. But, isn't it the case that there's a gap of an inch or so between the 45S diffusion glass and the negative? With the 45S being mounted above a filter drawer, I don't see how the diffusion glass could be any closer to the negative than about an inch higher. Assuming this gap exists, is this not a problem? Wouldn't there be significant light fall-off between the diffusion glass and a 4x5 negative? If not, why not? I ask, because I have a Type II Zone VI with the Beseler color head adapter, and the adapter is thick enough that the diffusion glass can't reach the negative. It finally occurred to me that this gap is probably similar to my conjectured gap with a 45S mounted on a Beseler enlarger. As I say, I wonder if this wouldn't lead to uneven coverage, too much light fall-off at the corners, etc.