Th advice we were given was not to put down any schools you definitely do not want to consider ,even if you have not used up all 6 options. If you do, you will be offered a school on your list( e.g.poorly performing choice 6) and the LEA will be deemed as having fulfilled its obligations and you are stuck with that school.
Conversely unless you have the independent option would it not be better to have a nearby potentially poor choice than falling through? Once that happens the LEA will still allocate you a school it will just be wherever there is space and that could be a poor school miles away. At least that is my understanding of how it works.
With regards to tfad and MHC. You are playing short odds. There are only 24 academic places on offer. I would imagine HBS is like QEB selecting the whole year group by academic selection so there is a greater chance of places. So hopefully that will work in your favour.