How to specify DRM/KMS the main connector (monitor) of the two?

Question

linux

It's about a bare console, without any graphical environment.
Two monitors:
1. FullHD (1920x1080) - via HDMI-A-2
2. UHD (3840x2160) - via DP-1.
When you start your computer, DRM/KMS selects the lowest resolution, namely FullHD. This is completely logical and normal in terms of default settings. However, because of this, only 1/4 of the screen area is occupied on UHD.
If you turn off the HDMI (FullHD monitor), then everything is in order on UHD.
Passing parameters to the kernel when booting in the form:

drm_kms_helper.edid_firmware=DP-1:edid/dp/dp.bin video=DP-1:3840x2160 drm_kms_helper.edid_firmware=HDMI-A-2:edid/hdmi/hdmi.bin video=HDMI-A-2:1920x1080

Does not help. (edid already did it here just in case, because it automatically comes by itself). Used various variations of these options, does not work if both monitors are connected. The conclusion is that when both monitors are on, the DP-1 cannot be set to a resolution higher than 1920x1080. However, you can underestimate both for DP and for HDMI.
Yes, the problem is solved by creating a systemd unit to start "fbset -xres 3840 -yres 2160" when the computer starts.
But I left this in case a native solution for KMS could not be found.
In general, how can I specify either the main monitor through KMS, or increase the resolution to UHD? Is it possible in principle?