I always thought that you measured equal distances for the length of a spike.

For a 6 pointer you would measure the length of the beam from the center line of the g-2 to the end of the main beam and mark equal distances from the center line of the g-2 towards the tip for the h-3and that distance again towards the tip fir the h-4.

example: center of g-2 to the tip = 6"
h-3 taken 2" from the center of the g-2
h-4 taken 2" from the h-3

That way your h-3 and h-4 would be taken evenly along that 6". (2+2+2=6)

I know for 8 pointers the h-4 is taken at half way between the center line of the g-3 and the tip of the main beam.

Maybe I'm wrong but I'll ask when I get mine scored in a couple of weeks.