Getting 240p scanlines from 480p games

[Nodoyuna]

Hi there

I have two monitors, a TV set for 240p and 480i games and a PC monitor for 480p and beyond

Anyway, as I like scanlines, I usually have an .ini in a separate Groovymame folder for displaying 480p games in 240p mode with scanlines in my TV set at 15KHz

In the ini, I have the modeline option activated, but I have disabled the generation of interlaced modelines
In this case, GM uses a modeline of 1280x240 that displays 480p games with scanlines
This works great with Groovymame, but now I'm trying to use the same method for other emulators...

I've tried demul, and if I set the desktop resolution to 1280x240 before running the emulator, it runs with scanlines, at least with Hikaru and Gaelco 3D games
I've found a program: DISPLAY CHANGER II, that can change the desktop resolution, run any program and when exit from that program, it restores the original desktop resolution

As I'm saying, it works great with Hikaru and Gaelco in Demul, but on Naomi games, the image is too compressed
Also, I've tried if with arcade pc games, like Deathsmiles II, but if I use my method of 1280x240, the game displays a 31KHz signal, but I can see it have indeed scanlines

Any ideas about why those arcade pc games does this?

Thanks in advance