Thanks for the reply TO,

Is it loss chasing - yes to some extent.

If we are upto bet 54 and the bank is $42 and the opening price is $3 then the bet to be made is ($54-$42)/$3 = $4. If the horse wins but only pays $3.50, then we have only returned $10.50 of the $12 hence our next aim is ($12-$10.50) = $1.50 + $1 = $2.50 (the added $1 is because we are upto bet 55).

If the horse pays $5 then we now have $42 + $20 = $62 in bank and we will stay at $1 bets until bank falls below the bet level.

I have chosen the 1st 3 opening favs as the likelihood of hitting a winner in the 3 is >60% (someone may be able to give a more detailed expected theoretical strike rate).
As I have said previously using the opening price gives us an edge as in most races we would expect the winners price to be greater (and sometimes much greater than the opening price).

Most bets are only at the $1 level.