(increased contact surface area per unit volume fluid
This is very true, there's another factor that comes into the equation.
With micro bore you get more hose on your reel. The more hose you have, the more coils on your reel, the more coils on your reel, the more it resists the flow.
Imagine firing a bullet down a straight pipe, if it doesn't touch the sides there will be no loss of velocity. If you fired it down a coil of copper pipe, it may still come out the other end but will have lost most of it's velocity due to it's contact with the walls of the pipe. Even water causes friction, as does air when it's pressurised. you can feel this for yourself when you pump up a bike tyre, and the sides of the pump gets hot.
Try this experiment. Measure your flow rate with all the hose on the reel, now measure it again when all your hose is pulled off the reel. You may well be surprised.
Dai