I've been flight testing my quad a bit and things are going smoothly.. but I've noticed when it gets out of sonar range (10-20) it will jump to 200-300 alt. I am wondering what the issue here may be?

I know in real aircraft I have to adjust the altimeter as it's based on sea level, and needs to be adjusted based on the ground level of your location. Is this true for ArduPilot? 200-300 meters may be about right that that case....

I went through the manual a few times but was unable to find a reference this this - that said, I can easily miss things!

Any input is appreciated!