Re: Length of heart
It's all relative. The perfect reed scrape (yeah, right) is such because of the balance between its three major parts: tip, heart, back. The thickness and contour, as well as the length, of these parts must work together to produce the feel and performance that you are after.
That having been said, for my reeds I think about the length of each part of the reed as a ratio of 1:2:4. The back is (approximately, I don't actually measure any of this) twice as long as the heart, and the heart is twice as long as the tip, measured down the center "spine" of the reed. This basic rule of thumb has served my well, so you might give it a try!
Let us know how it goes!
Owner, Marzluf Reeds