Screen positioning

Hey! I’m trying to recreate my old gbc on my tablet but being new to retroarch i have some problems that i don’t know how to solve.

Right now the biggest issue is the screen positioning. By the design of my background image (gbc) the screen is supposed to be 720x648 and must be moved 408px on the x axis and 164px on the y axis. But inputting those values on the video settings makes the screen have wrong position and scale. Here is a screenshot of this problem, notice the actual size of the screen on the top right corner. This is my config file, please let me know if you find something out of place or badly configured, i mostly just changed:

aspect_ratio_index = 22
custom_viewport_height = "648"
custom_viewport_width = "720"
custom_viewport_x = "408"
custom_viewport_y = "164"
video_aspect_ratio = "1.100000"
video_fullscreen = "false"
overlay_directory = "/storage/emulated/0/RetroArch/overlays"

Changing the values on the app itself is a bit cumbersome because you can only add 1 by tapping, I can’t lower the value, however i checked that the scaling and X Pos are working but the Y Pos isnt, the screen sticks to the top no matter what value i put in Custom Aspect Ratio Y Pos. What am I missing?