OK - my take.
1. As folks have said, where the silks end up is entirely up to where the string maker wound them to and how far the peg is away from the stop tail or stop tail part of the bridge. They will always end up the same distance from the peg once wound up to tune
2. The big no-no is not to have winds on the tuner riding up on each other...even a bit. If they do, it allows the possibility of the winds shifting in relation to each other and that could lead to tuning instability
3. The ideal is to end up - with all coils butted up to each other - having the exit of the last coil as near to the bottom of the peg as you can get (but without risking 2 above). This way, you maximise the break angle over the nut and - in the case of string trees - it applies less tension and friction onto the string tree
4. The actual distance to allow depends on how thick the string is and how thick/long the thin string leader is
5. In terms of the distance I cut to, I personally have a rule of thumb of a fingers-closed hand width past the far side of the post (which for me is 10cm/4"), but with the bottom E usually shorter in order to avoid 2 above.
6. If I am going to err on a 'safe side', I err towards longer and not shorter. If I've overcooked it, I have no problem loosening it, snipping a cm or so off the end and then rewinding it