Please expand the macro syntax

[Jackofham]

<stpt> was not in there anywhere, the closest thing I saw was /targetpc, which isn't the same.

<stpt> would be used in a way like this: /ac "Cover" <stpt>

When using the macro a subtarget would appear and filter everything except party members so you could search through your party for someone to use it on without taking your target off your current target or changing your target filters.

You can already do that on a controller without using a macro. While you have an enemy targeted, you can use the up or down arrow on the directional pad to scroll through the party list until you reach the player you want to cover, without hitting the X button use your cover ability, and your focus will shift back to the enemy you had targeted in the first place.