While working on a different project, I decided to meter the light falling on the baseboard of my Beseler 23C-II XL Dichro Head , using my sekonik incident meter in EV mode. To my surprise, the measure in the center of the board (below the lens) is higher than on the corners, in fact, there is more fall off as you move further onto the edges of the board. The fall off is between 0.1 EV to 0.3 EV. This is the case regardless of the height of the head. - Is this the reason I am getting a partial and light cyan cast only in the center of the picture which only happens at longer exposures. (it doesn't at short exposures) ? Is this fall off normal , and if not, what to do to correct ?