It is important to separate training from working. In one aspect you are always training a horse, but the difference is the focus of the ride. In a training ride you are working of a specific set of items trying to improve those attributes in your riding, while in a working ride, you sometimes short change things that are not working as good as you like to get the job done. The issues when you work with curiosity it you are always working between that curiosity and flight mode, so while you may use some firmness and accept something less than what you would like, you are still bound by that line that pushes the horse into fight mode.
You can only ask with so much firmness, before you have to accept that the horse was not physically or mentally ready for what you ask.
This spot never goes away in a horse. With some horses, once conditioned and trained it is pretty consistent, with other horses a long layoff will require a lot of work to get them back to a quality working level. Peppy is a horse that requires a lot of work and practice to keep in a quality campaign mode. Even out of shape and practice he is still a working horse, you just have to work around where he is at more than other horses. My old horse Heart was just the opposite; you could just get on him and go.