SAP PPPI-MES Z characteristic question

I have a requirement to create some z characteristics to be send to our MES system through control recipe/process order. Those Z characteristics are pretty simple, for example I need to read a field in MARA for the header material, read duration of a phase etc..

I did my home work on sdn and found out that if the logic is simple then I can just use the table and field (not function exit) in the characteristic definition (o27c). Here is my question

I need to assign a field in MARA of my header material to the Z char value that I have created. for example lets say I need to populate MARA - FEVOR. I have included this field in the table-field of the Z char in o27c transaction. This z char is assigned to ZORD_1 which is copy of AORD_1. standard chars in ZORD_1 are material number,order quantity, resource etc.. There is no plant or order number in this PI category. so how will system figure out howw to pick the FEVOR value and assign it to the characterictic? FEVOR is plant specific and I might have different value for different plants. will system pick the right plant? if so how will it piuck as I dont see any plant or process order characteriscitc in the zord_1 or aord_1 PI category.

Thx

Swathi