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.