Set up an Approval rule based upon the Non-recurring Element's Input Value

We have a requirement wherein, approval should flow on the basis of value ranges. For example, if the value entered by the Manager lies between $1000-2000, the approval should go to 2 level up managers.

The problem is with a Gross up element, where we are not using Amount field, instead, the user will enter the value in "Net Input Value" field. The approval fails as it does not get any value in Amount field. Is there a way to route the approval using "Net Input Value" field?

Thanks.