Help me to understand the decision to cap but sit outside capping circle

Tanitha: Hello's.
You don't need a "whole team capping" in fact 3 tanks cap at the same rate as 15.
So why have 15 tanks as targets in the cap circle?
In most situations 3-4-5 capping while the other 10-11 defended the cappers (outside of the circle in cover) would be more advantageous.
http://wiki.worldoft...turing_the_Base
/Tan