Thanks for the effort jtracc, and good methodology. I've had the exact same issues as you with 50/50 and 70/30 juices. Got 1 out of 7 heads to vape...flavorlessly.
These things just don't wick and I had come to the same conclusions as to why, but it's nice to see the evidence. The holes need to be bigger and less dense filler wrap on the interior. The filler material should just be there to draw liquid through the hole, but it doesn't appear it's capable of soaking up enough liquid for this purpose.
I haven't had the leaks, but the dry flavorless hits. I can see how the filler wrap can be the culprit for both situations. The filler wrap needs to be tightly abutting the wicking holes. If it isn't you will get juice inside the head between the wrap and the inner side of the cylinder leading to leaks, but you will be getting juice to the wicks (well the bottom wick/coil at least) and possibly a decent vape, but no flavor as there isn't enough pressure to draw liquid into the coil/wicks with liquid inside the head already. If the filler wrap IS securely abbuting the hole well enough, but isn't efficiently transporting liquid (due to the material) to the coil wicks you will get dry flavorless/wispy vapes.
Edit: Also, to someone who has a head they are happy with, and wouldn't mind sacrificing a head for a test. Would you mind taking it apart after some vaping and comparing the filler wrap, top wick/coil, and bottom wick/coil. I have a suspicion that only the bottom wick/coil is getting fed, not by the filler, but by liquid leaking between the wrap and inner wall into the bottom of the atomizer chamber and the top coil/wick will be bone dry.