I forgot to mention that another nice way to learn this is to cheat on turns.
You say you can fly strait across the field backwards inverted so when you get to the end and need to turn, instead of a nice smooth turn that will probably end up with too much aileron and most of the times knife edge (come on, ask me how I know
) you can just turn it with a sharp ugly turn by applying quickly and shortly aileron + tail + back elevator.
Ok, this is going to look more like a car skidding in a sharp turn but it will turn the heli 180 degrees and thats what you need. Do another fly by and to the same on the other side. After a few days you can slow down that turn a little and after a few weeks you can make them even slower until one day you will do wide open turns without thinking.
In my case I used to screw up turns so badly because of high speed and trying to do open smooth curves that I usually ended either doing a knife edge (forgetting to correct aileron) or doing an ugly pie dish (freezing). The quick ugly turn will at least ease your nerves flying in that awkward position (I still miss one or two heartbeats doing it though)
"Perfection and patience usually walk side by side..."