Thanks for replying!
In Encore, the Premiere sequence, when I right click on it and go to interpret footage, is automatically set at: Use the asset's par: sqare pixels (1.0). Changing it to any of the other options doesn't appear to make a difference on the Monitor window or Preview window.
Regarding my footage, for some reason some of it, instead of being fullsize (4096 x 2160), is 3072 x 1620 or even smaller. Anyway, I let Premiere Pro decide on the sequence settings based on the first piece of footage I put in the sequence, which was one of the fullsize clips. The settings include square pixels 1.0. By the way, I've (top and bottom) letterboxed the 16:9 sequence so that it's 2.35.
Any further thoughts?
Many thanks.
Dominic