Vacuum is a matter of ribcage position. The more "open" the ribcage is - the better vacuum. Also its about abs controll. Ribcage position can be influenced by training....there is an old technique for opening your lower ribs and repositioning the sternum - breathing squats. Heavy squats immediatelly followed by pullovers over the bench with emphasise to stretch in the top position. Sometimes followed by the vacuum....but this exercise only works till you are still in puberty - lets say till 16/17. Old people have no chance to fully use this thing.
I know because when I started as 14yo kid some old bodybuilder told me to do that and my ribcage opened and widened pretty well. Bad side of it is my ribs time to time.pop out of my sternum and I need chiropractor or massage therapist to put them back