What is a firm edge base?

Hello I commend you for a fully informative and educative website, crammed full of handy tips and facts. I am left, however a little confused about the difference between the different constructions of sprung bases; your article here seems to say firm edged bases contain the spring in its frame and that cushion top styles contain the springs in a layer?

I maybe misunderstanding but I had always assumed ‘sprung edge’ meant springs right to the edge of the base and ‘firm edged’ only to within a few inches or so of the edge and that otherwise there was little difference in the suspension layer?

‘Sprung edge’ seems to be confusing because I understood the springs were across the whole cross sectional surface area of the base (and not just the edge!). Most manufacturers do not seem to offer the choice of either designs, with some retail stores being puzzled about the difference. Notwithstanding the ‘roll off’ or bouncy tendency on the edges of a fully sprung base, they may provide more forgiveness to a firmer mattress but I notice you do not supply these. Can I confirm that your firm edge bases contain a similar suspension zone of springs (other than in the side frame) over the base?

I may be tying myself in knots, but it’s bugging me, so any clarification greatly appreciated. Kind regards, Chris.