the width of romans

cathy left a comment on the envelope with the overlapping romans
and it made me remember a question i have about the grouping of letters by width

i see width groupings
but J and K are not always in the same group.

MW -wider than a square
OQ -fit in a square
CDG - slightly narrower than OQ
HAUNT VXYZ - slightly narrower than the above line, do you put K here?
SELF PBR - halfish width, or do you put K here?
I-narrow - do you put J with I or with PBR?

are their any mnemonic devices or songs to help remember these letter groups?

this is going to be on an envelope.