I'd agree with the measurements given. One thing you have to take into account are the conditions at the time of shooting an arrow: at Agincourt before the battle with the French the English long-bowmen took their bow strings and put them under their hat to keep them dry in the rain as a wet bow string was pretty much useless. The art of archery is not as modern movies like to pretend by shooting in a straight line; you have to aim up so the arrow drops to the target. The average bowman probably had no idea of gravity other than something pulled the arrow down.
The English bowman was unique in Europe for the the level of training they had. By royal decree every male had to practice the long bow and it actually changed the shape of men's upper bodies over time: a century of bowmen produced much broader shoulders and these men could 'hold' the arrow at full draw, which if you have every tried archery is no mean feat. Other countries had archers too but none practiced as much as the English peasants were required to do (by the way, the armies of the day were rarely the King's own men. They belonged to the Lords and Earls and so on who owned land and would on request loan men to the King in return for favours and even money.)
The development of gunpowder, improved armour not damaged even by improved armour-piercing arrows led to a decline in the archer but for a time they were the mainstay of English armies. The great problem for archers was ammunition, in this case arrows. It was possible for an archer to shoot something like twelve arrows in a minute and thus it was possible to get through tens of thousands of arrows in a couple of minutes. It was hard keeping them supplied and archers often risked a lot to go out to collect their own, or other people's arrows in a battle. They would not have armour being peasants, other than leather jerkins and would carry a hammer rather than a sword if they needed to fight up close.
A short search for the range of an English longbow reveals that the average bowman can reach roughly three hundred yards of maximum range. However, that's with chances to hit only against large targets, not individual soldiers.
Half a bowshot in this particular case would be a hundred to a hundred and fifty yards (assuming, of course, your architects didn't really have an archer come up to demonstrate how far he could shoot). Not sure how that compares against castles in real life, though.