Maybe you're just noticing tw's more, though you likely are getting tked more often as well. Less armor means you take a hell of a lot more damage from friendlies than you otherwise would. From my understanding, team-damage reduction is on the raw damage side, which results in a much larger damage reduction than simply cutting the end damage in half. This means that in heavy armor, most TWs will likely just glance and you'll be much less inclined to remember ever being tw'ed.