Wouldn't
IF(lay_matched-back_matched-back_unmatched<.01,0,lay_matched-back_matched-back_unmatched)
be better than:
IF(lay_matched-back_matched-back_unmatched<.01,.01,lay_matched-back_matched-back_unmatched)
The bold expression will set the amount to zero if not it would contioniosly place a bet at 0.01 when there is unmutched bets?