Legacy Zebra nailed the rule here.
In real life application, the easiest way to remember PSK is that if the foul happened as part of the kick coverage, it's PSK. If it happened as part of the punt rush, make it previous spot.
There are sometimes goofy fouls that are part of the punt coverage, but by technical reading of the rule become previous spot (for instance an immediate hold of the gunner on a punt prior to the kick). By philosophy, make those PSK!