So you think using the same temp water you could get your wort down to a cooler temp if your input is at the bottom versus the top? Is that what you're referring to as "most overall drop?" I don't believe the "overall temp drop" will be affected by the inlet at the top versus the bottom. I only foresee the rate of drop being affected, which is why you would want your cold inlet at the top. Additionally, this will also create convection currents that vertically move the wort and therefore prevent any possible temperature stratification of your wort.Most overall temperature drop, no.
Excellent points. I have racked fluid with a persistent bubble in the tube. You would think the tubes are completely filled, but filling from bottom to top assures it.Cold water in at the bottom would help to fill the chiller completely, the bubbles will rise to the top and flow out.
Done the other way there has to be enough flow to push the bubbles down first before they flow out.
Bubbles in the tube reduce the heat exchange, probably not enough to matter but since you asked whether there is any reason to do one way vs. the other...