5e OGL by roll20 / MM compendium drag and drop bar error

I am using the 5e OGL by roll20, and have the MM compendium.  In my game settings I want bar2 to default to AC for all tokens created by dragging out of the compendium.  I see the field "Bar 2 value" with "On Default Tokens created by doing a Compendium drop onto the virtual table top, set the Bar 2's value to this attribute."  However, when I save the game settings with "npc_ac" or "ac" or "@{npc_ac}" all of these get me text in the bubble of my new tokens, not the translated value that the stat block of the monster should yield.  What is the issue please?

I don't have the MM to prove this, but I believe that you are supposed to use the Bar X Link instead of Bar X Value.

Kyle, thanks!  That did work.  I remain puzzled by the wording on the Game Settings page, as the "value" and "max" defaults also refer to using attributes to specify those values, rather than by link.