MU4 Position priority with voices?

In this snippet, I have two voices. I would like the quaver A to be positioned after the minim E/B. I searched on forums and I think this is related to z-index, but in MU4, this has been replaced with position front/back. However, I did not find how to modify this property.

I tried to exchange voice 1 and voice 2 (no effect on position), right click on the A note to find a property front/back, go to the property panel (F8) and find a relevant option...