Size 4 Korda curve with korda N-trap soft hook link, with 9 out of 10 times its bang centre of the mouth. My loop is inch and half long that goes through the eye of the hook. I always over weight the pop up. And yes targeting 30s and 40s. But I've obviously caught much smaller fish on it and it's still bang centre.
When I've used chod type hooks, I've had hook pulls, hooking in different parts of the mouth etc.