I just purchased and installed the game from the offline installer. The scaler value in that download defaults to normal2x at this time, for what that is worth.

I think the change you may be missing is under the "sdl" section at the top of the file. Change output from overlay to "output=ddraw" and see if that gets it working properly. You would need "fullresolution=desktop" in the sdl section as well, but that should already be there a few lines above "output" as default post-install. Also the scaler change to one of the hq values rather than normal, as you had mentioned.

I hope this helps with your issue.

Hmm,
i never got into scalers, but trues is that Gulikoza Dosbox build (which is ancient) base looks somehow much better Gog version - regardless of configurator settings.. i would be nice at least replicated Gulikozas quality..