Two things to make sure are clear:
- Atmospheric pressure varies with the weather, so the altimeter must be adjusted, or calibrated, to provide an accurate altitude above sea level. This is what the altimeter setting (or QNH) is for. The value 29.92 inHg represents a “standard” atmospheric pressure setting, but more often than not the actual altimeter setting will be a higher or lower value. If you set 29.92 everywhere all the time, you are not getting an accurate altitude all the time, unless the altimeter setting happens to be 29.92 inHg.
- Altimeters are meant to show altitude above mean sea level, not altitude above ground. Much of Europe near sea level, while much of North America, especially in the west, is significantly higher than sea level, so be sure you’re looking for the individual airport elevation. This can vary widely around the world, even within one geographic region.
CO73 is about 400 nautical miles northwest of KDFW, and is at 3610 feet above sea level. If you have the correct altimeter setting, your altimeter should read 3610 feet when you’re on the ground at CO73. You can set this automatically by pressing the B key.
It looks like your altimeter is actually working correctly.
If you were on the ground at CO73, at 3610 feet above seal level, and set the altimeter calibration to 28.20 inHg as you did in your screenshot, you would expect the altimeter to read around 1800-1900 feet. This is what we see in the screenshot. If you set the altimeter to the current altimeter setting, you should see about 3610 feet on the ground.
If you want to test this, you could go to KDFW, press the B key to automatically set the altimeter, and confirm you see about 610 feet on the altimeter. If the altimeter says ~610 feet on the ground at KDFW, it is behaving properly.