Bypass in the threaded end is likely better as the bypassing oil does not have to go over the dirty filter media to get to the bypass valve.
I remembered I have a bunch of cut open filters in my garage. So I looked them over. Of those with bypass on the threaded end, the Purolator (L40017) and Motorcraft were exactly the same, whereas Wix differed slightly in the location of the openings.
Essentially it is a round case with a flange about 2 inches wide that fits in the outlet end of the filter media between the filter media and the outlet hole of the filter can. All outgoing oil passes through the middle of these bypass valves, which is wide open (maybe 3/4 inch opening all the way through). Anyway, the input to the bypass is some holes around the flange area on the top. Bypass oil would flow back under the antidrainback valve and into the bypass valve. There is a metal spring inside the bypass valve, going around the exit hole part. The pressure has to compress that spring to open the bypass valve.
The Wix in my garage still had the antidrainback sitting on it. And in that case the antidrainback valve has ribs on both sides, the ribs on the back apparently to keep the antidrainback valve from blocking input to the bypass valve.
Another interesting observation is that the Wix had more clearance (around the filter media end caps for normal oil flow) than did the Purolator, Motorcraft, Napa Silver, and Fleetguard. Not sure it matters though as it should not take much space for oil to get through (you know how it comes out the seams in your engine all too easy).
