To tell you the truth, I have no idea if my calipers are long or short reach.

The frame/fork is built for 700c wheels and I am using 700c wheels so I would assume that these brakes are short reach (rather than 27" frame with 700c wheels)
By the way, my calipers came with the bike.

But what is happening for my is not "flex" but rather than the PULL of the brakes feel almost sticky and not smooth. (as apposed to snappy and clean)