I have quite a lot of comparisons fail because the other device hits the stop button.
Even with only the 625XT, I have done as Anders and pushed the button with my clothes.
It is also a little unnatural to push the buttown where it is now, thumb-index finger goes easily diagonal but not across the clock - not so well timed stops.
The natural position is to me opposite to the lap button, i.e. right lower side.