The hilite is a tricky beast. Sure its easy, set up the exposure from hilite to read F11, put camera to f8, Set main light to f8, job done. Well that's what they would like you to think !
But in reality it is NOWHERE near that easy :-(
The key is getting the hilite evenly illuminated. Set the camera to f11 with blinkies on and slowly ramp up the lights illuminating the hilite. The result will show you where the hilite is blowing out first. You should aim to get it all to blow out at the same time - this is impossible but is what you are aiming for. You should aim for no more than 1/2 stop variation over the whole area. I can just about get this with my 8x6 hilite and two strobes.
One that is done with the hilite just blowing out at f11 turn the hilite strobes off. And set up the main lights to f8.
Now take two pictures.
1) Main lights on hilite off
2) Main lights on and hilite lights on
The 2nd picture will show you where you are getting wrap and edge destruction. You aim is to make the subject in 2 look as much as possible as 1. Basically the aim here is to minimise wrap and maximise lighting independence between the main lights and the hilite.
The train is just about impossible to get white without throeing far too much light at it. The best bet is to get sheets of transparent acrylic and put them ontop of the train. That way you will reflect the light from the hilite and this will help LOADS - the lower you take photos from get the better it will be.
This is what I generally get to in the end - this has had about 15secs of pp applied in LR. It is NOT perfect there is still edge damage around the top of her head. But my studio is smallish and she is about 6 feet from the hilite plus with kids you just cant flag off the bits of the highlight you are not using. I have got black material on the white ceiling which helps prevent 'bounce flash'.