Thanks my Friend!
I hope I’m not being invasive. But I like to understand everything. That’s why I’m insisting here. I invite our friend @HyperspaceMadness to join the discussion. I’ll exemplify here:
For this specific case, my method is quite simple. First I start any game (NES for example). I go into the Retroarch video menu and make the basic video and alignment adjustments, which will be used for all systems operating in the 4: 3 ratio. To know the exact values of the screen, I use any overlay among those I intend to use. I usually write scale values on paper. What I have here are screen measures that I need. My overlays in this case, all have equal measures.
Then, I load any rom again and then, one of the HSM Bezel pack presets. After that, I make changes to the shader parameters to match the overlay I want to use. I make modifications only in frame + bezel + tube, without using any background from texture folder. I saved two versions of this preset and named them Global_Whit and Global_Black. Basically what changes between them is the frame color.
My background images will be my overlays, activated in the Retroarch options and not by the shader parameters. I use each of these presets according to the emulated system.
Then, I load one of these presets and then select a different overlay according to the emulated system. After making all the adjustments, I save presets to the roms folder. If the Core is exclusive, then I save a configuration per core as well. Lastly, I also save an override setting outside the shader menu.
Here my configs presets content:
Every time I start games from the same folder, the expected result will be the same for all of them. For each system, I will only have a different overlay. As in this example:
I chose to do this way because at this moment my hardware doesn’t perform well with the backgrounds “injected” by the shader itself. When I get a more powerful system, I intend to make full use of HSM Bezel’s features and all textures.
I can give you copies of my shader presets in a private message and you can analyze the files and perform the tests yourself. I believe that this will help to understand my doubt, which may be the same as others.