Hmm!
I don't think 4 bare 120w COB's at 18" would look like the PAR map above from 4 boards with 1 ft spacings.(same windmill layout like your strip build) Unfortunately I have no simulator but I'm pretty sure especially on the sides and corners the values would be lower with higher readings in the center in the same time.
Is it a lot of effort to test this in your simulator?
You know, I like both COB's and mid-power products like strips and boards. I would not use boards myself unless I had a lot of them and could literally cover the whole ceiling with low driven boards, lol. So I avoid them for the exact same reason like you.
I only say, the PAR map
@welight got from 4 of his boards is really good and you will lrobably need much more COB's to get something similar. At 120w per COB and 18" I would expect a higher hotspot directly under each COB and lower values on the periphery because the COB's have less LES and act like a point source.
Average readings would be identical, no question, they are both in the same range, but distribution, especially at a short distance, is better with boards. The also produce a center hotspot but not in the same way like one single COB.
With 4 COB's compared to one board there is for sure no difference. Cobkits tested 4 or 5 citi1212's against a single QBv1 and got even better results from COB's! A single 1825 maybe has similar average readings at 18" but for sure not the same uniformity.