@Weaver,
I've just taken a look at my 1312 and the top definitely does have ventilation too - it's in the vertical sides of the curved patterning if that makes sense.
So they are vented top, bottom and on two sides.
I would personally be very cautious about obstructing any of the ventilation as excess heat and electronics are not good bedfellows.
I appreciate that you are after any small gain in speed that you get, but would honestly be very surprised if any homemade screening will make a worthwhile difference.
Happy to be proved wrong of course.