by reading the help file "BACK-T1-IP"
lay at one tick offset lower when bet is matched and if the bet is not matched when the market goes in play then the bet will not be cancelled (including the original back bet and the offset lay bet)
thats will include the original back bet, may i know how can i place the bet in In Running only if the back bet is matched (so that it will not post the back bet again at In Running)?
The LAY bet is only placed when the back bet is matched so you there should never be an instance where the LAY has been placed without a matched back bet.