the biggest problem is that on Java app 320x50 banner would look good on any resolution, and on CocoonJS it will be big on i.e. 800x480 and terrible small on 1280x720 (and so on)
anyway: banner on top = -50% clicks, banner on bottom = +50% clicks; more touches in app = more clicks...
but as I stated in many posts: Java dev can make real money on entry ad + interstitial ad + banner ad + exit ad; and C2 dev can make pennies on AdMob banners. Quite unfair :)
everyone interested should mail i.e. email@example.com and push them to support Construct 2