The RTL docs say the vehicle will first rise by at least RTL_CLIMB_MIN or to RTL_ALT_M, whichever is higher, before returning home.

The docs already describe the RTL_CONE_SLOPE exception, but I could not find a note about altitude fence limits also affecting RTL return altitude.

In ModeRTL::compute_return_target(), the code appears to:

1. compute the RTL target altitude from current altitude, RTL_CLIMB_MIN, and RTL_ALT
2. apply RTL_CONE_SLOPE if enabled
3. then, if AC_FENCE_TYPE_ALT_MAX is enabled, clip the return target altitude again using the fence safe max altitude

Relevant docs:

• RTL: https://ardupilot.org/copter/docs/rtl-mode.html
• Fence: https://ardupilot.org/copter/docs/common-geofencing-landing-page.html

Relevant code:

• https://github.com/ArduPilot/ardupilot/blob/master/ArduCopter/mode_rtl.cpp

It seems the RTL docs may need a short note that an enabled altitude fence can further cap the RTL climb/return altitude. The corresponding PR is attached below.