Thanks for all the replies folks
Everybody seen the trebuchet throwing furniture flash game? If not check it out
http://www.skt-products.com/contents/hikkoshi.html
Anyway...
OK sort of makes sense (thanks for the link RAJ). So non offset = Bad and a Partial offset or full offset = Good. I am also of the opinion that any of these could be acheived (i.e spider sits secondary in the middle of the tube but it can go up or down the tube slightly as well as tilt).
No idea how I have mine set up up of course

but will try to find some pics of how it should look online.
Just did another quick photo of the inner rings for ya K Man (hazy - I was working with a size limit

).
.....then of course in another thread I read someone had the center spot marked incorrectly now wouldn't that throw a spanner in the works
Thanks again folks - it's appreciated