I don't think circle hooks are any better for flies for tarpon, in fact I think they are worse. Bait fishing certainly yes but not flies. All my guides have at one time or another tried circle hooks and reported that they just do not work as well as J hooks. I've been doing this for more than a decade now and I talk with good tarpon anglers any chance I get and all the good fly anglers I know prefer J hooks. With many of the good hooks out there I don't see a reason to even consider circle hooks - my hook to landed ratio is somewhere in the vicinity of 40-50% with J hooks.
Just an FYI, I've hooked tarpon solidly in other spots than what you've noted Juro. When they're hooked well in these other spots, they are hooked very, very well - it takes a lot of reverse pressure to pop the hook out of these areas of the tarpon's mouth.