Nominally the bottom bar should have a rebate depth of 8mm (beespace).
The top bar should have a rebate depth of 17mm. This is comprised of 6mm, the height of a standard metal or plastic runner, and 9mm which is the height of a standard top bar. All being well, the top bar will sit on the runner and be flush with the top of the box.
When inserted, the bottom of frames will be level with the top of the bottom bar rebate, which is of course 8mm from the bottom of the box. Most definitely a bottom bee space box.
Without the 6mm runner, the box would of course exhibit 6mm of top space, but that wouldn't make it a top space box.
I hope this helps to clear up any doubt in your mind.
I do realise that my arithmetic is 2mm out - sorry, call it working tolerance, as the runner probably sits slightly high.