The distinction in most old photo books was between 'small tanks' (a few rolls of film) and 'deep tanks' where the film, on racks or hangers, was lowered into the tank. The terms 'large tank' (= opposite of small) and 'shallow tank' (= opposite of deep) rarely if ever appeared.
Three major differences are first, that with small tanks, the tank is normally filled and emptied, while the deep tank is left full and the film lowered into it (much faster, more even wetting); second, that with deep tanks, the developer is normally replenished so that it soon becomes 'seasoned' (quite high bromide levels) implying reduced true ISO but very high consistency; third, agitation is obviously very different, and this is why the manufacturers refer to 'small tanks', implying inversion or 'twiddle' agitation rather than raising/lowering the racks or using nitrogen burst. Deep tanks were normally covered with floating lids when not in use, and the developer might only be drained and replaced at astonishingly long intervals.
Obviously with multiple rolls the distinction starts to become blurred, but as there is no such thing in most of the literature as a 'large tank' you can make up any definition you like. Indeed, at Ilford, 'small tanks' were sometimes used like 'deep tanks': the tank filled, and the film dropped into it in the dark before the lid was put on. The important point is agitation, and that's the same for a 1-reel 'small tank' as for a 6-reel or 8-reel 'small tank'.
Cheers,
R.
