My PC's motherboard is 'micro' ATX but its physical measurements are 9.6x9.6 in. So the label 'micro' is clearly irrelevant. Show us a credible source that says an engine radar blocker has openings in the cm range.
It is not nonsensical. You used many phrases and words today that you did not used before when you came here.
Now as for the 'round nose' bit...
The ogive as a RCS compact range standard : Dominek, A. : Free Download & Streaming : Internet Archive
The ogive is a well known standard shape used in calibration, qualification of new measurement facilities, and in aircraft designs. Which part of the ogive in my debunking of you that you do not understand? Heck, did you even know of this?