Using baro height with optical flow guided mode

Hello everyone!
I’m discovering optical navigation modes with my small quadcopter powered by pixhawk and arducopter 4.1.1. Attached optical flow sensor up-flow" and 12 m lidar rangefinder.
Loiter mode based on Optical flow sensor (without GPS) works very good - copter hovers in place stable, when moving coordinates track shown in mission planner, i can even navigate and return home via mission planner.
FlowHold mode does not perform as good as Loiter, copter is shaking around, navigation is not possible.

Problem of Loiter optical flow is height limit by maximum rangefinder distance, but why I can’t use baro height instead of rangefinder at >12m heights? If I’m flying over flat surfaces (flat horisontal field) for 5-10 minutes. Atmosphere pressure is stable and fly height from surface is known from barometer. Why we can’t use this height source if lidar is out of range at big heights?
Is it possible to change some settings to use optical Loiter with baro height source?

Thank you!