3/4 bike lengths is ok, main concern is safety, half wheeling is a no no. At the end of the day, if i'm going at my own pace and they decide to draft and pass me later on -so be it, providing they don't pass and then go slower/hold me up. Equally I think it's ok to pass someone (safely) when they are slowing down for a junction, and I have a better view/assessed the situation/in the right gear etc, not everyone takes the same time as others assessing the road situation. I don't own the road so fully expect there to be other cyclist/road users too, I do follow another cyclist (not wheel sucking) like following a pacemaker, it's just like following the speed of traffic in the car. This can be misconstrued differently by other cyclist, that's fine, because I can't go around telling everyone I meet on the road what I and how I think.