Hi Markus,
you can expand moaic under Mosaic and Research Section in Voyager, just add panel on the grid.
If you want to expand in WebDashboard you must get the same center and create a new mosaic with the number of panels you need for sure all the panel center will be different. Also you create a new panel mosaic expandi the previuos just positioning right the center, get the new panels and add to your previous mosaic and research sequence.
All the best
Leonardo