Thanks very much for your interest.
I refer mainly to the UK channels (but same applies to all other channels).
BBC One broadcasts in both SD and HD.
With SD all is normal. With HD the same subtitles become huge and at very inconvenient locations in the screen (obscuring the view)
With the Cisco HD Recording Box I was using up to last week this was no problem as both subtitles were the same size.
I have checked with other people I know and this is an issue only occuring on the Horizon box.
see pictures of the problem in 2 different channels