@SupraSPL says ->
https://www.rollitup.org/t/gonna-do-my-first-diy-led-with-cree-cxa3590.854157/page-3
At 700mA (51W), a 12-20" spread between COBs is doable, depending on the canopy size you need to cover. If you are planning on using active cooling, for (4) CXA3590s (204W)
-3.5" profile - 46" length
-4.23" profile, 36" length
-4.6" serrated, 17.5" length
-4.9" profile, 25.5" length
-5.375" profile, 17.5" length
-5.88" profile, 23" length
-7.28" profile, 17.5" length
-8.46" profile, 15" length
But if you are thinking passive cooling, with a little help from your circulation fan, basically triple the lengths above. I am still experimenting with reducing the passive cooling numbers though, you might be able to get away with a lot less if your circulation fan is hitting them.
peace