Hi @Iain Robinson,
Thanks for sharing the detailed explanation of the issue. To better understand and investigate this, could you please confirm the exact version of InDesign you're using (from Help > About InDesign) along with the details of your operating system?
Also, if possible, a short screen recording showing the behavior you're experiencing, such as switching between presets and the "Import as Static Text" checkbox not retaining its state, would be really helpful for us to review and check further with the team.
Looking forward to your update.
Abhishek