Overlay.

Generally when I look at an event, I have a bet of x amount if the overlay is 10% and then for every amount the overlay increase by 4% I will increase the amount I stake.

I nearly always bet on the asian handicap markets in the Football so the bets I place are mainly between 6/4 and 4/6. However this is my question. I have just started betting on the 12x in matches where betting a team to win outright is better value than playing the handicaps. For teams at big prices, of say, 9/1 should I increase the overlay before I have a bet? I am thinking this becasue a 10% overlay at 9/1 is only 1% of value which leaves no margin for error

Maybe increase the overlay to 15% if the price is bigger than 6/4 and 20% if the price is bigger than 4/1??

Any help would be greatly recieved.

thanks