I think it is, but I do know that they can't calculate your TER equivalent score without your Written English score, so maybe it is your overall score for your MC component that you use after all.

I guess when you have two components (Written and MC) they must work out the average between the two to serve as your TER score perhaps? Coz my TER score is between those two scores. I didn't even think that it might be worked out that way as I only had my own scores so didn't see a correlation until now! D'er.