Substitution fails...in RBA

Hello,

I am running into a problem in Rule Based ATP.

In our Check instructions for Rule based ATP Check, I have selected 'Create Remaining Requirement for Source Location product'. My assumption was this:

1. Material A Req Qty 200

2. Material A Stock 100

3. Material B Stock 50(We can substitute this for Material A)

4. With the above setting I thought I would be able to create a planned order for Material A(we have CTP running) for 50. Unfortunately the system ignores Material B completely and creates a Planned order for Material A for 100. Flabbergasted.

If this is how it is going to work, then there will never be a substitution. Am I missing something?

Thanks in advance,

Subash Nanjangud