I really do not know the answer to your question. In most cases you are looking to maximize the bass output to balance the mid and high end. You can use a back loaded horn to offset the baffle step but as you say the size becomes an issue. I don't see any easy way to get the volume of bass required to run a speaker system without a BSC circuit without it becoming very large like a back loaded horn. Bass reflex, TL's, TQWT's and closed boxes do not seem to produce this type of bass volume.

Martin