Then have some other rules about as long as all 4 are ranked in the top 16 (or 20) and they played at least 5 actual road games...

If necessary allow up to 1 of their conferences to have a 5th team if they all 5 are ranked in the top 16 (which ever conference has the highest ranked 5th team available). If there are not 9 from within those 2 conferences in the top 16 then they only get their 8 max.

So even if they got all 9 in that still leaves 7 bids (currently 3 auto to the next 3 best conf champs) with 4 being at-large available to the other P4 (ACC/B12) and Go6 (AAC, CUSA, MAC, MWC, PAC, SBelt). And some years they may not get to 9 and therefore 8 other bids would be out there.

But honestly at only 12 team play off they should not be able to monopolize 8 spots and only leave 4 total for other conferences.