leaky b-post

Hi everyone - after a triumphant summer of leak repairs (silicon sealer having put an end to the deluge through the rear light fittings, front light fittings, map compartments, rear air-con outlets etc etc), i have just one water source left to deal with - out of the (top) seatbelt hole on the nearside b-post (2001 TD5 ES)

is there a generally accepted "usual" position where water finds its way in to create a problem here ?

thanks in advance