Doesn't matter. If you have a VE you get stamped in for 45 (30 again soon???) days and you have to have 30 days of coverage. A TV gets you 60 days so you need 2 months of coverage. If you come in on a new Non-O (retirement) you'll be stamped in for 90 days so have to have that much coverage. If you have an O-A or Non-O giving you a year's entry then you need a year's policy. It's tricky right now and could get expensive if you make the wrong choice.
I also found out more about the required return flight. According to TAT's Phuket Sandbox General Information page: "If the length of stay is less than 14 nights, travellers must also present a confirmed flight ticket out of Thailand."
But surely the time left on a visa is the maximum permitted ? No-one knows at that point if you are going to renew it or not do they, so how can they demand more ?
Also Faz wrote this on the covid insurance thread
The Covid Insurance must cover the period of stay granted on entry.
If you are returning on a re-entry permit on an extension based on retirement then the Covid Insurance must be valid until the renewal date of your extension.
??? - Apologies if this is going off piste