Would you consider two mixers, a lower one for the bath and a higher one for the shower so there is no confusion for visitors?

Safety and ease of operation should be the highest priority when looking at mixers for shower/bath combinations. If you only want to have one mixer then make the height suitable for somebody having a shower. You don't want to be bending over to adjust the temperature when showering in a shower\bath. I usually design bath mixers and spouts centered on the wall of the long side of the bath so if you need extra hot water when you are having a long soak it is easy to reach.

I have never heard of the requirement for a bath mixer to be at 700mm, although this could be a good height for a bath spout depending on the depth of your bath.

Best of luck with your new bathroom,
Dr Retro
of Dr Retro House Calls

I have a shower over bath arrangement, and have had for a few years now. My advice is to have the shower head and bath spout line up at one end of the bath. But have the mixer centred on the wall mid bath. That should give room for a fixed shower screen, at the spout/head end with plenty of room to turn on mixer without getting wet.

That’s my exact plan- glad your advice backs me up! I just need to work out how high to place the mixer..?

I’m a bath person so mines at the height that I can reach whilst I’m still reclining in the bath but don’t have to lean over too far to turn on for the shower. It’s roughly 500mm between the top edge of the bath and bottom edge of the mixer.