Stretch emulators to fullscreen

[mmmRetro]

OK... here goes...

I am running recalbox on a RPI3 with composite out connected to a 13" tube television. Most emulators have black bars on the sides only. Is there a way to stretch these emulators so that they fill the screen entirely like they did on the original consoles?

I have adjusted the overscan values to get emulationstation to fill the screen correctly, hoping that this would make the emulators follow suit, but no dice.

Any help is greatly appreciated.
Thanks

[mmmRetro]

Here are examples, the only one that truly outputs to fullscreen is GBA

http://imgur.com/a/4n2gW

Also here are the contents of my boot/config.txt and recalbox.conf

config.txt = http://pastebin.com/6jCPaged

recalbox.conf = http://pastebin.com/Zie8EjbL

Thanks again.

[mmmRetro]

figured out that i need all retroarch emulators to be displayed in 3:2 aspect ratio. now to figure out how to get them all in that without having to create a custom config for each emulator.

[Substring]

@mmmRetro you can find the parameter name for the retroarch.cfg file, and add it yourself to /recalbox/share/system/configs/retroarch/retroarchcustom.cfg. It should work. The file is xan also be found through the windows network shares

[mmmRetro]

adjusted this line. finally figured it out

aspect_ratio_index = 6