sorry for coming in late to this - been on holiday
but fyi......

2012, SD, runtime 151mins as per sky - 1.37GB
2012, HD, runtime 151mins as per sky - 5.40GB

28 days, SD, runtime 99mins as per sky - 928MB
28 days, HD, runtime 99mins as per sky - 3.56GB

just the first 2 examples for info and yes its just some movies that are HD downloads, but one good thing for the slow speeds like me - let it download about a minute for the SD stuff and you never catch up with the download so can watch in real time, HD stuff need a few minutes more to ensure no buffer

Many thanks for the explanation and confirmation.

Cheers