Control parameter for instant PR creation by saving the Sales Order

[reck]

Dear Experts, 

i have a doubt regarding PTO process.

With the combination of TAS as item category + CS as schedule line category, i can create an sales order with a material ( even without MRP view )  . By saving this order , a purchase requisite would be created immediately. Yes i know this is a typical 3rd party process. But i am curious, which parameter controls this automatic flow.

I know to enable the whole process we need quite a lot parameters in customizing and material master data, but i am more interested in the immediate action of creating PR. Is this because of the setting in CS (e.g. Ordert type NB ?) , or any setting in TAS,  or even the requirement type on position level in my sales order ( i checked the requirement type is empty ).  ? 

The reason is we may need a similar process to create a one-on-one PR for sales without MRP run, and  we need to create Z category and types to enable that. Thus i need to know which parameter trigger this immdiate creation of PR, so that i can set them correctly at the correct place.  

Thanks in advance!

Regards