Simply because the WA pool is so small. The Quinella pool is not combined with other TABs and increasing my bet actually affects it.

For instance, the winning combo for today's NZ race 7 was $116.80 from a pool of $730. That represents $5 on the right pair (ie $730 less 20% commission = $584 divided by Quin odds of $116.80 means $5 was bet on winners). Had I bet $1 then Pool = $731 less 20% = $584.80 over $6 leaves $97.45. Had I bet $2 my winning would be ($732 x 80% / $7) x $2 = $167.30. This is better than $97.40 but I risked double, ie I am 14% down. Spread across a day, if my average daily gain was 10% (I wish!) I would actually turn a winning day into a loser merely by increasing my bet amount.

Now, not only does doing the same thing in Qld give me a whole other pool, the pools are generally much greater. The same NZ race on QTAB had a pool of $3,127, over four times greater. The winning combo actually returned $177.70, but for the sake of argument, if the win was $116.80, ie approx $21 of winners. Using the same maths, adding my $1 would reduce this to $113.70. Doubling my bet would leave $108.80 ie I am 7% down, meaning I could maybe increase my average bet without screwing the pooch.

Incidentally, the Vic TAB Quinella pool for the same race was $3,886, paying $89.50 and the NSW pool was $4,408, paying $192.70, therefore I would like to have a go at these and any other TABs also.