it's kind the nature of the beast. The solution would be to spread out the lights, because there running at 120 degrees and all your par's in the center. All your ppfd is having them up close, it's built into the design. Also, you don't want to get too high or spread out on these lights, the best thing, is to button them down, close as possible. Like you say, either the 2000's or even 1000's would be the way to go, depending on cost. Or maybe even a mix of different ones, to fill in the spots, but clearly the 4000's are on the extreme of the footprint for that for that particular wattage.
Personally I think re-engineering them, spreading them out would do huge things, The quality is there. (allowing it to be put closer, over a bigger area) but the cost would have to reflect that in materials, I suppose. That's why I was suggesting another line to him actually.