Panels in 3rd party aircraft don't usually have MINIPANEL entries. They use the default mini-panels according to type. As an experiment I tried the Cessna 140 I installed recently.
This is the normal mini-panel view.

The same aircraft after a quick edit to the default Panel.cfg.

This is the edit;
[MiniPanel00]
position=7
size_mm=600,100
window_size=0.9,0.20
child_3d=1
background_color=0,0,0
ident=MINIPANEL
gauge00=MiniPanel!Airspeed, 0, 0, 100, 100
gauge01=MiniPanel!Turn Coordinator, 100, 0, 100, 100
gauge02=MiniPanel!Attitude, 200, 0, 100, 100
gauge03=MiniPanel!Heading Indicator, 300, 0, 100, 100
gauge04=MiniPanel!Altimeter, 400, 0, 100, 100
gauge05=
MiniPanel!RPM Indicator, 500, 0, 100, 100