EGA monochrome (mode 0Fh, 640x350x2) doesn't work correctly. I mentioned it to HAL-9000 not long ago, and there may be a fix at some point, but it's low priority. Armor Alley and a few SubLogic flight sims (Jet, UFO, MSFS 3.0) are among the few games that will use mode 0Fh; however, they support several other modes, so mode 0Fh is not a necessity.
The simple solution is to use hercules graphics instead. If you really want to see the games mentioned above in mode 0Fh, running the attached workaround program in DOSBox should make the mono graphics visible with an EGA or VGA machine type.