@Jakub
I did an adjustment in the FPGA core to shift the picture a bit to the right. I used a real A500, kickstart V1.3 and an initial cli screen with standard preferences (no devs:system-configuration file) to have native screen orientation on both system.
The new setting in Beamcounter.v at line #59 is:
parameter hsstrt = 25; // front porch = (uncalculated)us (25)
Now the horizontal screen start is 100% accurate to an ocs/ecs Amiga.
Also the H-Sync signal now has 15.52KHz as on a real Amiga (before it was 15.62KHz).
Would be nice if you can implement this setting in your next core