As far as I know they work the same as Hi focus.
I would guess its just easier = cheaper that way.
On the US side most MFGS sold a 14" probably all with the RCA
jug. RCA also had a 19" low focus, Zenith 14" & 16". Most used taps & a few
a control to adjust. After a few years you usually didnt see a
difference adjusting them unless the CRT was VERY strong.
From Japan TONS of them were sold through Sears. Mostly
Toshibas & Sanyos. They looked even worse but on the test
jig not so bad at all after you put a hand full of low
level tubes in them.
73 Zeno
LFOD !