Hi Oz,,,got some interesting advice from a full time punter ..

He stakes depending on how much his top rater is ahead of the next rated horse,,
example..
Black Ink 2.80
Sir Monashee 5.5
Foxmore 6.20
Black Suit 8.50

his top rater is 2.7 ahead of the next rater ..he would then have a scale
1.5 / 2 he would outlay $100
2 / 2.50 $200
2.5 / 3 $300
ect

so in this case he'd have backed Black ink for $300

I like his way of thinking and have been phantom trialling this recently for some good results..