On rotary knobs like HUD Brightness only the second half on an axis is used. I tried multiple input device (Virpil CM2 throttle and Total Control MFBB). If an axis is mapped to the HUD Bribhtness knob axis the knob only starts turning when the knob or lever (both axis devices) has already been moved halfway. It makes no difference if the Axis Tune has "Slider" checked or not.
For example, DCS recognizes an axis as -100 to 100 and HUD Brightness only turns and does something in the range from 0 to 100. Now checking "Slider" in the "Tune Combo Axis" changes the input range to 0 to 100, which should match perfectly, but now the knob only turns from 50 to 100.
The same controls work as expected in other modules and I tried multiple input devices. This seems to be a bug with the F-15E?