i like to work a spall all the way around before i decide on the point. if at all possible, i try to use the thinnest side for the back so its easy to get the shaft on.
also, if your spalls are big enough, try to knock some longer flakes off and use those for your arrow heads, those flakes will make some realy good arrow heads and can be a lot easier to work than a full spall.
in my opinion, there are different types of heads. Flake heads and spall heads. both seems to work very well. flake heads are made from a thin flake and a lot of the time dont have flakes running all the way to center. somtimes they are the best heads, but they are nt as attractive as a head with flakes all the way across. and ofcourse a spall head would have the knapping markes across the whole face. because it had to be thinned across each bi-face.
look at these 2 heads, (although its difficult ot see) the white one is from a small thin flake, normally thrown away. and the black one is from a spall. the white one has a "bald" patch in the middle, it was already thin enough through the center. the black one had to be thinned. the white one is just as sharp if not sharper than the spall head.
i guess thats not really what you asked, i just hoped i could share something i learned with you.- Ryan