That doubling up staking plan works fine if one does not have any long runs of outs , which eventually happens & thats when the tear drops start, not fair I know, but fair ain't got nothing to do with it.

Try this on Favs
Must be highest in place rankings.
Must be Fav priced $3.30 & less on TAB.

This improves its SR dramatically.
40% SR
Stats show -8% LOT at level stakes using TAB prices.

Make selection using TAB figures but make your actual money bet with either...
Betfair ,for best value.
or
Betezy best of 3 Totes or something similar.
They allow bets as low as .10 if need be.

You may like to try the Retirement staking plan (Google it)
Only with a twist , which is ,reduce its divisor by the rounded up decimal odds price of the winner rather than its fractional odds (e.g. 2/1)
e.g. if its price is say $2.50 , we make it 3/1 , now deduct this of the previous divisor used.

It now crushes this plan into profit where at level stakes it may show a loss.

The idea of the Retirement plan is to start again as soon as any profit is made.

__________________
Cheers.