Thanks Kerik and Sandy; My unit was made using 4 of these:

Not elegant or super efficient but consistent and no problems up until now. All of bulbs are evenly spaced (1 3/4" or 2 1/4": sounds's upstate now and I'm down) and the lights are now about 6 inches from the print. Here's the kicker- looking back at earlier prints of this negative that I made with a far better 'engineered' unit 'the problem' was noticeable-though far less so- because I printed it much lighter and split toned it. Couple this with the fact I noticed this issue with another Bergger BPF 18 negative and I think it comes down to Sandy's explanation-it's the Bergger film (tray processed)