Installing pc fans on cobs

Hey i have a problem i cant figur out and need some inputs for the best result.

I have the vero v7 cob lights with big heatsinks on. I whant to lower the temperatur for each cob and im installing pc fans on toppen of the heatsinks.

What would you do draw the air out from the heatsink or blow "cold" air on them / flodas

Always blow down toward heatsink

I would attach a sheet of tin cut from HVAC ducting to the back of the heatsink with the fan mounted in the middle.