Can you just answer the question? Resolution and color depth. This is necessary information when releasing RTG game, so users can create a P96 screenmode for it.
#define RTG_MODE_ID 0x50FF1000UL
```
And the UAE config uses an 8-bit RTG screen:
```ini
gfx_width=864
gfx_height=486
gfx_colour_mode=32bit
gfxcard_type=ZorroIII
gfxcard_size=16
rtg_modes=0x3ffe
```
So the app opens a custom 8-bit Picasso96/uaegfx screen at `864x486`, using `BestModeID()` first, falling back to `0x50FF1000` if needed.
The "gfx_width=xxx" line is setting from the UAE config file which determines the emulator window/screen size.
The Amiga program knows nothing about the existance of these settings, so it makes zero sense that the Amiga app opens screenmode based on these parameters.
Also, I tried your UAE config+hdf setup, and it doesn't use RTG at all. It opens the game in AGA NTSC interlaced hires mode.