Hey Stu, not sure why the kicker should be so high, you basically only need it to establish on the problem from a sit start.
Here are some other sites with some construction plans:
The uncarved block
board is too overhanging (60deg) but they do have a concave and convex board deign.
system is really cool. The board is 40deg overhanging and once you've obtained the grips you can download problems from the net and set them up on your own wall. No a system to use if you're coming back from a finger injury since the holds are pretty small in general and you're not going to find any slopers in the set. The downside is that you need quite a lot of vertical space (about 3.5m).
In both of the above wall designs the kicker is no bigger than 370mm.
Anyways hope this helps!