Sorry if these are dumb questions.....Not very educated on transponders.....looking for some clarification/education.

I hooked up my used garmin 327 to my used MGL oddessey. Quadruple checked the wiring and all is good......A question I have is, the pressure altitude on the Garmin 327 is based on 29.92, so unless the pressure in my area is 29.92, it's not going to display my actual elevation of 250' on the pressure alt display?

What the EFIS has displayed when I adjust for field elevation or local pressure is not going to match the pressure alt display on the garmin? Unless everything is 29.92?

So an example is today, I set the EFIS to 29.92 and it shows zero as my elevation. (actual pressure was 30.19) My garmin displayed 0 ft pressure alt. So this seems like it matches. As I increase the Baro setting on the EFIS, it changes, but the Garmin pressure alt does not. Makes sense that this stays constant. But.... how sensitive is the pressure altitude supposed to be on the Garmin? Yesterday, pressure was 30.39 and my Garmin 327 was still displaying 0 ft. Today it is 30.19 and still showing 0 ft. Seems like the pressure alt should be changing with that much of of a difference? Or am I way off base here?