It seems your understanding of the use of the warbow in the late middle ages is somewhat flawed and you are basing a number of misconceptions upon these flaws. According to modern scholarship, archers never loosed their arrows in regimented volleys as we see in films and television and the like. We have no period records of this style of organised shooting. The only period references I am aware of relate to a single signal to start shooting such as Sir Thomas Erpingham throwing his baton in the air to signal to the archers to start shooting at the Battle of Agincourt. In fact this style of volley shooting would be almost impossible and highly impractical with heavy 100+ lb draw weight warbows as you can't hold them at full draw for any length of time. Testing a bow at 20 metres is also perfectly valid. Again we have no evidence of archers ever arcing their arrows at a steep angle to shoot long distance as is done in many films and television. All period depictions that I am aware of; unless it is a siege and the archers are shooting at enemies on the top of a wall have them shooting level and straight at a relatively close range. This makes sense as tests conduced by scholars have found that the power of a loosed arrow from a warbow is at its greatest at 20 metres. As archers can shoot relatively quickly you want them to conserve their arrows for when they have the greatest chance to do maximum damage to the advancing enemy therefore you must wait until the enemy are as close as possible and then having your archers loose all of their arrows as fast as possible in that range where they will do the most damage, leaving no time for volley fire as such.