I find they come up quite small. I buy XL even though my horse doesn't have particularly big ears! As mentioned before they are not very generous across the crown, especially once they've been washed, hence going up to XL
I also find they come up small. I get XL for my 15.2hh ISH. They also shrink after washing... and the acoustic ones seem to fall off at the shake of a head. They were lost out hacking a long time ago now
I stitch little loops onto all my ears and pop the throatlatch through them. (This is after having to hop off on several hacks to retrieve some hi-viz ears that had been sent flying.)
Mine do come off and the bridle comes of with them I did a thread last week asking how people stop it from happening, luckily there were a few ideas I have yet to try ?