Wow, thanks for all the answers.
Ideally, the best solution is to have a 5 or 10 mm spacer above the stem. The top of the fork would sit 2-3 mm below the spacer. That way the fork will pass through the entire section of the stem and clamping forces will not compress the end of the steerer. If you have a stem with a low rise you might be able to achieve this by using a stem with more rise and moving a spacer from below the stem to above.
Due to my less than hypermobile physique I need as many spacers under and as few spacers over the handlebar as possible.
Or using a bung like the KCNC unit that has a larger surface area that extends from the top of the steerer and through the bottom of the stem, allowing for equal tightening force across the claming area.
checked this on KCNC's homepage - looks like a good idea but I can't see how it will fit down the steerer tube on my Colnago EPS, there is no shim or anything that kan be removed - or have I misunderstood how it works?
Lubing the threads and heads is actually a no-no.
this is quite surprising to me - I have always had it pounded into me that you must never use dry bolts on a bicycle.
So for the OP you want to check the gaps is somewhat even before you start (I use a 2mm hex key or something small).. apply same number of quarter turns alternatively to each bolt and finish with the torque wrench, ready to ride... don't think people bother to measure the final gap, do we?
The gaps start the same but the gap at the top is markedly smaller than the one at the bottom after careful alternate tightening.