I don't see why it needs to be so complicated (?) why not just use a fresnel lens to spread and even out the light -if done properly (?)
This was the basic plan - a quick sketch I just did for the purpos of communcation...
the top is a section and the lower a quick sketch to show the zone of cutaway- that occurs in the negative carrier, upper and lower stages - just using an angle grinder - I used a jigsaw for the 6x9 carrier plates I modified... seems like it just might work...
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