I'm pretty sure that each of the above is played and there's no "normal".
For instance we do based unit and area terrain conventions around here. in all the above scenarios we'd consider it blocked if the shortest distance from the attacker to target base crossed any part on the WE base (to keep us honest we use an empty base for landed flyers to sit on).
I'd categorically state that anyone that did the exact opposite of what we do
is a heretic to one true methodology is just as correct

These local variances can widely effect the results of testing (and not in a bad way-each has their + and -) and should be noted in our play tests probably.
I'd love to hear your conventions, mate!
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