Hello!
The neck of the horse is like the needle on the gauge that will tell you if a horse is working correctly.
This means that:
- If the horse is paddling out behind, the back will go hollow and the neck will come high.
- If the horse is stepping under with his hindquarters, the back will lift and the neck will drop.
It sounds like what you've got with your horse is going nice. For the time being, try not to get stuck in the 'poll must be the highest point' rut. That is true, but don't rush into it.
Before you ask for the horse to bring the poll higher, he must consistently be feeling downwards in his head and neck. The feel on the reins must feel consistently like the weight of the rein (and no more!) is being 'pulled' down. Not outwards, and not diagonally. Downwards. This is when the horse is on the bit.
Now, when he is working consistently like that, and you can feel his neck going downwards (try not to look to see his neck going down, try to feel it in the reins), now you can ask for him to lift the poll without evading the bit.
Maybe this helps, maybe it doesn't, but it definitely works if done properly!