Alternative item in BOM

I have one FERT material BOM, which has two ROH-1 and ROH-2.

Now in BOM for first ROH-1 I has below settings:

AltItemGroup - 1

Priority - 1

Strategy - 2 (100% check)

Usage prob - 100

While for BOM item-2 ROH-2 has below settings:

AltItemGroup - 1

Priority - 2

Strategy - 2 (100% check)

Usage prob - 0

Now my requirement is ATP should check stock for ROH-1 first if there is no availability then check for stock of ROH-2.

Creating process order for FERT material but system is not checking stock of ROH-2. If ROH-1 has stock then it confirms otherwise missing item availability message.

Can you help to understand what am I missing here?

I already check below forum or link but somehow not getting clue. Thanks in advance.

Alternate Item in BOM

https://scn.sap.com/community/erp/manufacturing-pp/blog/2016/01/18/alternate-item-group-concept-in-bom-sap-pp

Concept of Alternative Item group functionality in BOM

Reply appreciated.