Ah, I feel you, that’s tough. With belt, it’s something that we can fuss around with once we’re all the way up there…It’s breath, sound, GO, and hope you make it to the right now. Really, all I can say for this is to really visualize and internalize that note as you’re working. Additionally, letting yourself practice without stressing out too much about the note. I feel like this happens a lot with tough notes, like the E6 in Phantom, where people know it’s coming, it’s going to be tough, and then they tense and it becomes impossible to hit. It’s so psychological, so I encourage you to try to relax into it, because your mind is probably making things even harder on you!
Another tip would be to take it down a step or two in practice, work on hitting it in the lower range, and then work your way back up. That way you can really internalize that interval each time as you increase the difficulty, and hopefully that will make it easier in the key as well! Hope that helps!