The ideal amount of glue for each tab varies based on size. As a general rule, you should fill the entire surface of the tab.
Once applied, you should notice a thin, even bead of glue around the edge of the tab. This bead of glue ensures the tab has minimal potential failure points by ensuring a vacuum seal is formed between the tab and the panel. Uneven glue application causes air pockets that will weaken the adhesion and allow the tab to release prematurely.