with it been a new selection there is no variable for the amount that is bet on another selection.
there are a few ways to work with it.
you would have to put all the selections bm amounts,like this
(init_bet+s_1_bm_backa+s_2_bm_backa+s_3_bm_backa+(up to the maximum number of selections))
or you could use the balance and funds available, like this
(init_bet+IF(test_mode=0,balance-total_funds,test_balance-test_funds))
this will place your initial bet amount plus any other bet amount that has been placed.
mcbee