I honestly dont think board size matters at all, nor the bar...
Small boards can shoot up and get caught when kite is low and you crash, just as easy as bigger boards in my experience, in fact easier as I believe we use the smaller boards in a lot more wind than the big ones, so statistically a lot more risk just because of this itself
I can not see how the throw matters, as you typically hold the bar while the board shoots up between the lines when crashing at speed downwind or in jibes/failed maneuvers at high speed downwind, particularly when kite is low as said
But it can also happen when trying something new, say a toeside 360 with kiteloop or similar, and the board might shoot up in the lines when you fail and have no idea about where you nor the board "is", because you can not do it (as I can not...)
I think the best thing is not to panic, and try to control the kite "calmly" even when caught in the lines, and get it down on the water slowly (OR, in lighter wind, get the foil free while flying the kite)
Now and then some has cut their lines when the lines come around their foil when caught - this can happen too of course.
I have been lucky to avoid this, nothing but luck I know.
It seems, with experience it hardly never happens nomore - but can only speak for waveriding and freeriding and maybe I am too conservative (not taking chances) and not learning fast I know.
I dont know about racing and freeracing, if worse or hardly never happens ?
It IS a sketchy situation when it occurs, having the "AXE" ready to kill you so to speak, if the kite loops
Must say, if caught in the lines I would not trust the flagging to work every time as it can get stuck in odd ways or even loop initially, and it might end up in a more dangerous situation than if you didnt - so also sketchy whether to release or not
Best advice would be to wear a helmet IMO
Problem with "Foil caught in bar" is, I believe we all have experienced this, but only a few times, and these situations are VERY very different so maybe not possible to draw any general conclusions nor advice
Except wear a helmet and impact west, eventhough I dont myself...