Not local to QEB, but the Admissions Code http://media.education.gov.uk/assets/fi ... 202012.pdf
states the following:
2.6 Applying for places at Sixth Form - Children and their parents applying for sixth form places may use the CAF, although if they are already on the roll they are not required to do so in order to transfer into year 12. Admission authorities can, however, set academic entry criteria for their sixth forms, which must be the same for both external and internal places. As with other points of entry to schools, highest priority in oversubscription criteria for sixth form places must be given to looked after children and previously looked after children who meet the academic entry criteria. As stated in paragraph 1.9 m) above, any meetings held to discuss options and courses must not form part of the decision process on whether to offer a place.
I can't find any references on the QEB website to a Sixth form admissions policy, and yet one would think that a "cull" of the sort you mention could also create vacant places? Those vacant places would therefore trigger a requirement for a published 6th form Admissions Policy.
BTW, paragraph 1.9 m) reads as follows:
In the case of sixth form applications, a meeting may be held to discuss options and academic entry requirements for particular courses, but this meeting cannot form part of the decision making process on whether to offer a place.
It may be shot in the dark, and as I say, I don't know how QEB operates, but the Admissions Code is the legal framework you need to guide you.