X11 and Qt scaling configs not respected (OpenBSD 6.5)

I use the same version of MuseScore on two systems with the same OS and window manager (cwm). One features a display with a physical DPI of around 183 (3840x2160 in 24 inches). I have the Xserver and Xft.dpi values set to 192 (2 x 96) and these environment variables are set in .profile:

export QT_AUTO_SCREEN_SET_FACTOR=0
export QT_SCALE_FACTOR=2
export QT_FONT_DPI=96

With these settings, MuseScore looks correct, along with my other Qt apps (LyX and SMPlayer). The effective working area is equivalent to a 1080p display which is comfortable.

My second system has a display with a physical DPI of around 167 (1280x768 in 8.9 inches). The working area would be too small if I set the scale factor and DPIs to be close to the physical DPI, so I chose a factor of 1.25x (120 dpi). The effective resolution becomes 1024x614.4 which although small, should still be workable with maximised windows.

export QT_AUTO_SCREEN_SET_FACTOR=0
export QT_SCALE_FACTOR=1.25
export QT_FONT_DPI=96

LyX still looks fine and the fonts in MuseScore are correct too, but other UI elements in MS are being scaled higher than 1.25 (at least 1.5), no matter whether I use a mix of environment variables and command line options in the hope of counterbalancing the behaviour ('mscore -D 80' combined with 'export QT_FONT_DPI=120 mscore' and 'export QT_SCALE_FACTOR=1 mscore').

My inclination is that MS is prioritising the reported physical DPI over everything else.