Approval based on Grate Rate Midpoint

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Hi Experts,

I have a requirement to create an approval rule for the following condition,

AOR should get FYI if "salary > grade rate midpoint", I am able to find the attributes Grade rate min and Grade rate max but I am unable to find the Grade rate midpoint attribute. 

Is it feasible to create this rule, if yes can you please guide me on how to do so.

Thanks,