Flow stress

Hello

I am working on a thesis project dealing with flow stress in cold rolling, a plane strain operation. To determine the flow stress, tensile tests were carried out. I am aware, that the engineering strain/stress hast to be transfered to the true strain/stress and then the true strain/stress from the tensile test has to be mulitplied with the Von Mises yield criterion to yield the correspondent compressive flow stress in the rolling situation.

But i dont know which strain from the rolling reduction I have to input into the flow curve which is determined by the tensile test.

For example: if, during one pass, there is a reduction from 3.5mm to 3mm in rolling, resulting in a draft of 0.5mm and a strain of (3.5-3)/3.5=0.143, can i input this strain directly into the true stress-true strain curve to get the true flow stress or do i have to modify the strain first, to "translate" it from the rolling reduction (compressive, plane strain) to the situation in the tensile test (uniaxial stress)?

I would be very thankful if anybody can help me with this problem.