Multiaxial neubers correction

Hello everyone, I have a query I hope you can help with understanding.Based on Prof Mark Barkeys lectures on plasticity I have been able to develop an excel code for neubers and ESED correction. I also have referred papers on same by Glinka, Ayhan. I am testing my code against the research paper.I see authors have tested calculation against FEA and experimental results. They have used shear strain, however, they have not clarified anything on whether they are using engineering shear strain or tensorial shear strain.Also some authors have shown a nonlinear stresses are higher than linear stresses. Is it feasible condition?I am a bit confused on this topic, hope you could clarify on this. Thank you