File 1 +2 --> IDOC scenario using BPM

HI Experts,

    I have a scenario like Header & Item multiple line item files at source side and have to generate multiple IDOCs (Sales Orders). For this, i designed BPM ,with multiple mapping (2:1) , Now i can able to generate multiple IDOCs . IDOCs should be decided based  Order number in source files (correlation based) . But , based on mapping ,how to divide header and line items to each particular IDOC ,how to do mapping ?

I tried  : Order number (H) --> remove context --> sort --> based on value change --> collapse context --> IDOC structure and

             Order Number (L) --> remove context --> sort --> based on value change --> collapse context --> E1BPSDITM

Can you let me know what is the right process?

Deva