Curious signal strength situation

[Brooktop]

I have a Panasonic TUCT20 FV box which I've moved up to the bedroom because my new NTL Digital box covers virtually all the same channels. Each room has its own dedicated aerial but the one for the bedroom is pointed at a far off transmitter.

On normal aerial, BBC 1 and 2 receptions were poor, ITV 1 and Ch 4 were average and 5 was perfect. Now I've plugged the FV box in and run the auto set up (there doesn't seem to be an option to tune individual channels), I find that BBC1, BBC2 and 5 are perfect but it's not even tuning ITV or Ch4; positions 3 and 4 are taken by BBC1 and 2 again!

Seems odd. Anyone know why, or a way round? I can't get on the roof to change the angle/position of the aerial becuase my roof is about 50ft up. Can't really be bothered paying a £50 call out charge jsut to get it moved.