I wasn't totally convinced by the guy I spoke to at BMI or his supervisor (they always refer to a supervisor when I call, I must be trouble) so I sent an email to get the answer in writing. The answer is that the BMI website is wrong, the guy I spoke to and his supervisor are wrong, coz BMI DC give you %50 mileage when booking W with TG. Me happy now, me make booking :-)

They said in the email they would update website. That's nice.