It takes practice! The start line sets up the rest of the search so it’s a very important part of any exercise. I do the same thing in agility, BTW! I can get lost way too easily. 😉
Keep in mind, by asking the dog if they’re “ready” you’re putting the focus back on you, so I would encourage you to do that silently. 🙂
Also, I would definitely start working with the leash indoors with Paxton. I think if you work the threshold exercises it might help him to focus. You don’t need to hold him long. I let my dogs release themselves but they MUST be quiet and still. I watch for them to be attentive and then they know they can release themselves. Sounds like you’re doing that for the most part and that’s good!
Joyride K9 Dog Training