Manual Z-Seam positioning

Hey Community,
I am trying to get rid of the cracks and visible z-seam lines in my model.
I was playing around with Luban’s positioning function, but that left me clueless:

I wanted “just” to position the seam on an inside corner on the backside of the model.
But using the “back”, “back right” and “front right” positioning just put it to the front of the model.
I honestly also did not understand the x and y positioning options, since its not even clear, where the front and where the back of the model is.
Luban does not show anything in the preview.
Did anyone do some research yet and can explain, how the manual setting is positioning the seam and how the offsets influence this setting?

Thanks!

In Cura, when viewing the Preview, there is a Play button. It will show you the 3DP print head moving for the current layer. Where it starts is your Z seam.

I remember Luban having a play button too, but I don’t see it now.