Problem identifying Recalbox partition

[Defiant]

Hi!

I'm having trouble identifying the Recalbox partition so it'll boot directly into Recalbox instead of booting NOOBS first.
I just want to get rid of the "press shift for Recovery" screen with the raspberry logo.
I created the autoboot.txt file in my SD in Windows and wrote "boot_partition=6" in it as adviced in forums, but it had no effect.
So, which is the partition I'm looking for?
I tried every single one of them, from the logical ones to the extended ones, from 0 to 8, with no effect.
What am I doing wrong?
Here's a screenshot of my SD and partitions just in case.
Thanks a lot in advance!

[Substring]

@defiant is that a noobs option ? In which file have you added the boot_partition ?

[Defiant]

@substring in autoboot.txt, I read that should do the trick. But it didn't.

[Substring]

@defiant you dropped it on the very first partition ? Any official documentation on that feature ?