The Grecians have only conceded one goal from open play in 2013 and kept their second consecutive clean sheet in the 3-0 win at Morecambe on Saturday.
Coles, along with central-defensive partner Pat Baldwin, goalkeeper Artur Krysiak and left-back Craig Woodman, have barely missed a game this season while Steve Tully and Kevin Amankwaah have both had spells at right-back.
"It does help when you have consistency, it really makes a difference to me," Coles said. "Defensively as a team we are doing all right. It is not just the back four, it has been the whole team.
"Woody has been a consistent figure, and there's been myself and Pat with the right-back position shared a bit. Kev Amankwaah has come in for the last two games and he has been outstanding.
"Whichever right-back we have in we know we have a good understanding among the back four with Artur behind us. Touch wood we seem to be making less mistakes as well."
The City squad have been unable to make the most of their Cat & Fiddle training ground in recent weeks due to flooding and the freezing temperatures, and Coles is glad the boggy pitches are beginning to dry out.
"It has been really difficult for Tis and the team to sort out sessions for us because everything is too wet and the astro can be too hard," he added.
"It is a bit of a pain but hopefully the worst weather is behind us and we can have a little bit more consistency with training."