This just quick musing on Line of sight issue's that crop up during games.(no doubt some body else uses this method I'm just stating how I problem solve this grey area in gaming)
The simple answer is your mobile!Most phones have a built in camera these days.The lens is normally 12-15mm and 20-30mm from the edge of your phone,depending on which way you hold it.Ideal for figure hights.
place your phone infront of the firing model (resting phone on the table at the right hight.to aggreed upon by everyone before the game,ie phone to be placed on its side or on its end.this stops magic los from the top of a ladder)
doth the same from the target facing back towards the firing model.Then compare the images ,zoom in if you can see your target problem solved.
It also makes you look at your game from a completely new angle,and gives you first person views of your game and some great pictures you'ld never think of taking otherwise.
I hope you find this method useful(and I'm telling Granny how to suck eggs!)
Mark