The main issue here is that the only firebog houses left are mainly the little 3,500c bottletree houses and less than 15 of the 5,000c bottletree houses, So if you want a 7,500 you're out of luck.
I deduct that the main reason so many people want to live in the firebog region is because of the resources only found here(jellisack,fireflys,etc) and to grow herbs,and the reason for larger houses being as always larger houses having more plots. An easy way to solve this issue would be to add more/larger houses to the firebogs. discus below