I don't understand why the default aspect ratio is some weird figure that's never used by anything (it's slightly wider than 16:9 apparently) and thus has to be changed every time you load a new channel.
The best thing to do would be automatic aspect ratio switching between 4:3 and 16:9 depending on the content, like most Freeview boxes do. Presumably there's a tag in the video stream somewhere that tells these boxes which aspect ratio to use so surely it would be possible to tap into that?
If this isn't possible then it makes more sense to make 16:9 the default, considering all new programming has been in this aspect ratio for years. Better having to switch to 4:3 manually sometimes than having to switch to 16:9 or 4:3 every time you load a channel.