Hang in there and keep asking questions. One of the best ways to learn what's what.
Your colleague is observing the fact that the sums are based on the higher temperature and should be reasonable if that temperature existed. However, if the actual temperature is lower, you are going to get to the reject point quicker (ie less roll) than for the higher temperature case.
End result is that, for the reject, the actual numbers will be somewhat shorter than the assumed temperature calculation numbers and your pad will be greater than the assumed temperature calculation indicates.
As the ambient temperature gets closer to the assumed temperature, this difference will reduce progressively.
I'd be a bit wary about believing distances to the metre. A bit of conservative rubbery-ness probably isn't a bad idea.