This is just my curiousity, It happens all the time. I try to contact someone and lets say it takes ten, a second try might take 12 then another 11. Is contact somewhat random in the amount of stun it takes up?
I think whether you're standing, sitting, resting, what you're resting on...
how comfortable you are, maybe makes a difference.
If you're typing it one after another, take into account how much stun you may or may not have regenerated while you couldn't type in any commands.
Actual stun can vary from attempt to attempt, but all things being equal it will never vary more than 1 or 2