AFAIK if you make longer upper arm, closer to paralel arms setup, the camber will be less but base (distance between tracks/wheels) change more on turn, and traction of outside wheel will be worse; and this is reason the paralels are not used from '60s or so. And you add some weight on arm, I guess, it always worsen traction and comfort a bit.
Other hand, short/long arms, as standard MN12, is widely recognised as best compromise for base/camber stability. So - its no reason to change this point, I think.
Dodge Shadow '88 2.2 auto
Scorpio Ghia RS '91 2.9 auto
Merkur Scorpio '89 2.9 manual Explorer '93 40 auto Vitara '95 1.6 auto Thunderbird SC '89 5.0HO auto
Fiero '85 2.5 auto
I believe Boni was refering to both front and rear.
To answer your question, if you make the upper arm longer you will get less negative camber under compression (like the outside wheel under hard cornering) and less positive camber on extension (the inside wheel under hard cornering).