Michael I think you will find that the exchange prices are now often longer than they previously were as punters are also laying your selections on the exchange, & in doing so they are matching up many of the lay bets that previously would have converted to SP if unmatched at the jump.

Anyway there's an easy way to check & that would be to calculate your % returns since you moved to the larger stake, for example yesterday I believe there were 11 bets so -

$103.16/10989 = .939%

If you do this daily & list the results I would be happy to create a graph to display if your returns are diminishing or not.