I'm sorry if I'm confused, but let me quote I guess:

"If either of a character's armor ratings exceeds his Body x 2, apply a -1 modifier to Agility and Reaction for every 2 points (or fraction thereof) that his Body is exceeded" (149).

This is from the Shadowrun 4th Ed Corebook.

Just wondering, does that mean a char with Body 3 would suffer a -1 to Agility and Reaction if he wore an Armor Jacket (8/6) because of the 8 exceeding 3 x 2 = 6?

That sure does limit armor options for those not willing to sack up on the Body score (*cough* my mage most likely, *cough*).