Here’s an experiment that does when you want. It uses words instead of pictures because it’s easier to upload the experiment this way, but pictures would use the same approach.
In doing this experiment, I discovered a bug in SuperLab 4.0.5 that explains your confusion. When a Location trial variable is created and then you go to use it in the Event Editor, it does not appear to be there. But in fact, it is there. If you create five Location trial variables, you’ll find that the popup menu contains five items, but they are blank. This bug has been fixed in-house and will be part of the next release. It does not affect in any way the running of an experiment.
Words at Random Location.sl4 (4.1 KB)