Packaging Liquids for FBA

Relatively new seller here. We’re sending a gel product into fba. Product is gel a room temperature and does not turn to liquid unless heated >150f. Product will be packaged in a 500ml(16.9oz) boston bottle but only 400ml(13.5oz) of product will be contained within the bottle.
My understanding is that liquids over 16oz need to be in a polybag and liquids below amount can just have a tight fitting lid and shrink band. My question: Is the requirement based on overall weight of the item, actual liquid volume contained within the bottle, or net capacity of the bottle weather filled to that capacity or not?

edit: bottle is plastic, not glass.