To get Armor Transfer 3. 10,000 armor energy points to get to Tier 2, divided by 10 a kill comes out to 1,000, then 10,000 more points for Tier 3. At 20 points a kill for that one, it's 500. So, to get 3 it requires at least 1,500 kills with Armor Transfer on.

Retriever 1-3 takes 500 kills, Aim Enhance takes 350 while ADS, Rapid fire only 500 again, and there's others with similar requirements.

Why does Armor Transfer have such a steep requirement to level it?

Because you don't have to have it equipped to level it up.

I always wondered why. The same goes for heavy weapon pro. Why do all other modules have to be equipped but not these two?