You may be mistaking the terminology. I did, for a while.
Three types of magnet assemblies are found on Marquees.
One has only an adjustable flare ring pair.
One has flare and stig rings.
The third has flare, stig, and 6 pole, AKA triangle) magnet rings.
If you have the first type, you don't have a two pole magnet.
If you have the second type, you don't have a four pole magnet.
If you have the third type, the third ring pair alone is the six pole magnet.
Its purpose is to help shape the beam. As the name implies, it controls
the triangularity of the beam.
I've played with all those rings and seen what they can do, and they can
make the spot look like a perfect triangle with razor sharp edges, and they
can make the spot look like a triangle with cropped tips, and they can make
the spot look like a funnel pointed in one direction or another, and much
more. Personally, I believe that it wouldn't be that difficult to make a
magnet assembly that focuses the spot to MUCH finer spot sizes you can
get now, due to the power of these magnets to shape the beam in such
bizarre ways. I'm tempted to experiment, using tubes that are already
damaged and can't be hurt much more. Maybe an extra electronic focus
ring of my own design, hooked to a signal generator and amplifier....or
maybe just a variable DC power supply.
Might be a fun experiment. Just have to be careful not to focus the spot
size to a needle tip because it's then an instrument of phosphor and maybe
even glass destruction. This COULD be why spot sizes are limited to a
certain lower size limit in the first place.