That Airspace AVOID looks good. Some of the screen shots show altitude. I guess that's GPS altitude. How does that compare with barometric altitude?
Tony,
Others have given you some of the limitations of gps altitude. However it is often device dependent as different hardware manufacturers correct for altitude in different way.
In order to counter act this (so that you have a correct altitude for airspace warnings) the PocketFMS Airspace Avoid app allows you to enter your real Baro altitude, and it then works out the difference and applies that difference for the rest of the flight. This should ensure that the altitude that it uses for airspace warnings is very very close to your baro altitude.
Indeed the more powerful PocketFMS system also allows for a similar correction for similar reasons.
dp