The paper presents the use of an optimization routine in order to find the best combination of free length and fibre angle in an unnotched Iosipescu test processed with the virtual fields method. The sensitivity to noise coefficients arising from the special virtual fields procedure are used to build up a cost function aiming at balancing out the different coefficients of the three main orthotropic stiffnesses so that the same confidence level can be reached on these three stiffnesses. Then, experimental validation was performed using an ESPI system. Full-fields were measured and stiffnesses identified and compared to the usual 0 degrees, 30 mm configuration. The outcome of the optimization was confirmed by testing the same specimen several times and comparing scatter between the two configurations. This is a first promising result on the way to the design of a new test for orthotropic stiffness identification on a single specimen from full-field measurements.