It's curious that you've not reported racing sparks. It's always been said that the use of a helical primary will result in too-high coupling and racing sparks. Maybe no one's ever actually tried it? I hope so, yours is very compact!
To Gary,
I once tried a helical primary which was very similar to Jeremiah's primary on my research coil. It had the same compact appearance. It gave the same results as the flat primary provided the coupling was adjusted to the same coefficient in either case. It did not have any more tendency to cause racing sparks than the flat primary.