"...the slots in the cover from manufacture still have the spacer washers fitted" --> so the ventilation seems still not enough with this small slots in the cover. Seems the CNC milling solution from the italian producer could be a nice way to solve this problem.
I am sure the CNC milled cover will solve the problem but the washers are only a few pence and work as well. Any ventilation improvement will be a bonus, I doubt you can have too much.
