Changing X coordinate does not work

My problem is one of the most basic you can get: I have an object on a master page and I want to change it's X coordinate dynamically.

Apparently this should be pretty simple:

$.x = "100mm"

in FormCalc

or

this.x = "100mm"

in JavaScript

placed in the form:layout event should do it.

However, despite trying different events, it simply won't work.

Changing the width property "w" DOES work.

I was already told that my form should be saved as dynamic, and I changed the preview properties accordingly, but still I do not see any result.

Do you have any idea on what I am doing wrong?

This should be pretty simple to test, but I'll give more details if it's not clear enough.