[RobinH]

Andy,
Each manufacturer tends to recommend a particulur number of shims etc as a starting point. However I would say that the practical steps for any individual car are to check, in order..
1/ As Ian says above, check the bottom wishbone is cranked the right way for your car. In this case he suggests to the front which is the same as for an AK. This sets the whole scene for how far forward/back your wheel will be within your wheel arch. Forward looks a bit strange to me, but it seems to be what most chassis are setup for.
2/ The total number of shims used at the top should be selected to ensure that the top arms sit squarely on to their pivot arm. Too many or too few and they will strain the bushes. This might vary as bushes do.
3/ Unless you are using the holes halfway down the upper arms for mounting bump-stops, you have total freedom to use the arms either way up and swapped from front to rear, with your allotted shims (see above) in any combination of infront or behind the upper ball joint. This gives quite scope for variation as you have perhaps found. What you are aiming for is a combination which a) will give you your desired caster angle, which like Ian also says above will affect the self centering and load on your steering (~5deg) and b) will not protrude in such a way as to be too close to the inside of your wheel rim.
Idealy the shims would be equally shared, front and behind the ball joint for maximim flexability in the future but that I would suspect will be a 'nice to have'.