difference between SAP Universe and NON SAP while creating variable

Dear Experts,

I have generated Report by taking Universe on top of BI.

I have created a variable like--> Major Head=substr([Commitment Item];6;2).

But it is not working properly in case of using keyfigures.

But the same variable is working fine in case of NON SAP Universe.

Can you let me know what is the exact way to create variables in case of SAP Universe?

Thanks & Regards

Venkat