Thanks for the BA, Guy_98!
As an aside (in case you ever find yourself in this situation), you can still mount three 140mm fans on the top of the Switch 810 while still having the Corsair H100 mounted there as well.
Basically mount the H100 as per usual (on the "underbelly" of the top of the case). Go to a hardware store and grab some 1 1/2" #6 machine screws. I got the ugly Zinc ones, because they came with nuts for each screw, but I painted them with black metallic modeling paint so that, after they dried, it didn't look out of place with all of the other screws.
with 1 1/2" #6 screws, you can screw 140mm fans on top by screwing in FROM the top, rather than the bottom. Just an FYI - NZXT 120mm fans were out of stock and I had two extra 140mm fans, so I 'made it work'. Cheers!