Help identifying an artillery Field Regiment flash

[Skara Brae]

I recently came across this Royal Artillery Field Regiment arm badge or flash (with the numeral 4 in the photo).  A bit of research indicates there were four such badges, and that all four of these numbered flashes (1-4) are probably associated with the 55 Division. The one with the number 4 may be from the 4th West Lancashires. With some research, I was able to identify which Field Regiment of the Royal Artillery wore each of the flashes with the numerals 1, 2 and 3, but I'm stumped on the numeral 4.  I could only narrow it down a bit to (I think) the 5th, 170th or the 192nd Field Regiment (?). Can anyone please help me pin this down?

 

Also, when I first saw this flash, I though the red-orange shape behind the yellow numerals was the number 4 as written in Arabic, but now I don't suppose there's any connection. It looks sort of like a lightning bolt too.  Does anyone know the significance of the orange shape behind the numerals?