Relative to the frame positions vertically
The frames in a beehive are shorter than the box they fit in by a "bee space". If the frames are level with the top of the box and the bee space is under the frames this is termed "Bottom Bee Space" (BBS). If the frames are level with the bottom of the box and the bee space is at the top it is termed "Top Bee Space" (TBS).
All non - British hives I have come across are Top Bee Space. B.S. Smith hives are Top Bee Space. B.S National and WBC hives are both Bottom Bee Space as standard, but can be converted yourself, or by special arrangement with the manufacturer. I have never seen the British Standard for Commercial hives, but to the best of my knowledge all those currently made are Bottom Bee Space, although I understand the standard allowed for either. All other British hives I have seen that were commercially made, but had B.S. frames were bottom Bee Space.
There are claims and counter claims for TBS/BBS in the U.K. but having used both extensively I really don't think the claims for TBS are as great as they are made out to be. There are slightly different techniques needed for both and I am talking mainly about National. I changed all mine myself some years ago.
With TBS you really need framed queen excluders and I find the wire ones the best. The main benefit I find is the frames in the lower box don't get stuck to the upper box so much.
It would be a mistake to have a mixture of TBS and BBS because the gap will be nothing or twice bee space. You will either get the frames propolised together or a bigger gap filled up with comb.