As a bowler, 'what is a good length'?

At Cricket training, a few weeks ago, Graham, a good batsman, was bowling to other batsman, whilst awaiting his turn to have a knock. He asked me 'what is a good length for a bowler to bowl?' Bearing in mind this guy had played to a good standard, Surrey 2's, i thought he was trying to wind me up. After probing him on his thoughts, i soon realised he was genuine, he didn't know what was a good length to bowl a Cricket Ball. He has bowled a few overs in our 3's and 4's this year but was just trying to 'not get hit out of the ground'. I asked him to think from the batters perspective, what length would he not like the bowler to bowl. That, is then deemed a good length. For all batters the length will change, variations in height of batter and bowler, competency of the batter and pitch conditions all have an input. If the pitch is damp or hard the bounce will then vary, making the way a batter plays any given shot slightly different. If a batter plays the short, bouncing ball better than a fuller pitched delivery, then the nearer to the batsman the ball is pitched the better the length. On a recent coaching course the bowlers were asked the same question. Each was given a cone to place down on the wicket, to show where they thought a good length for their bowling was. The cones were placed from 1 metre away from the batters crease to 8.5 metres away from the crease. They can't all be right. Well actually if the conditions suit the bowler maybe they can all be right. As i have already said, every bowler is different, height, pace, type of delivery, how the ball comes out of the bowlers hand and quality of the batsman all affect 'what is a good length'. The ECB coaches handbook shows a diagram for good length Cricket balls, with a range of between 2 and 8 metres away from the batsman's crease. I don't think i fully answered his question but by asking him to think from the batters view point, he was able to find out for himself. That is what coaches should do, get the player to find out the answer themselves, with clever questioning from the coach. They then, can become independent and think for themselves during matches.