Hi there! Is that possible?
I think you are talking about this settings right?
Lx4 PAL (1080p50) (Generic 4:3 mode)
1. Increase H. Samplerate to 2200 and H. Active to 1920.
2. Decrease V.Active to 270.
3. Increase V.Backporch until you get picture (approximately 28).
NOTE: TV needs to be able to force to 4:3 aspect ratio.
If aspect ratio still looks off, try H.Samplerate 2460, with both H.Sync and H.Backporch around 215. Source
Alternatively, if you cannot force 4:3 you can attempt a Lx4 1440×1080 50Hz 4:3 image: increase H.Samplerate to 1900, H.Active to 1440, h.sync 150, h.backporc 212.