Maybe I'm just lazy- but I'd probably just lift the light if its lumens thats bugging your clones.
If it's temperature then you need to think over your room temperatures- I have a 600w passively aircooled that hangs only ~6-8" above the canopy.. that said, those are hardened mature plants, but a 400w a bit higher shouldn't be a problem (aircooled that is).
But seriously.. you could buy things, make things, redesign things.. but if you're cooking your plants the easiest solution is to lift the light a bit.