If you are planning balanced field, as most Boeing stuff seems to do, you are assuming TODA=ASDA (or usually TORA=TODA=ASDA). There being no stopway at Bristol your second sentence falls away, it can't be both balanced field and take account of a clearway that makes TODA longer than ASDA.
Surely said company uses all airport data such as TODA etc to arrive at the max possible take off weight?