pretty sure Chiang Rai requires 12 months, but that could be due to my bank book lacking detailed transactions, as I’m not in the country the entire year.
I just used my January, 2024 passport expiration date to shorten my extension period to 10 months, which moved my visa extension date from March to January, as they will only extend up to your passport expiry date. If your passport expire date and remaining validity are favorable, that may work for you.
At the risk of stating the obvious, print the e-visa paperwork and don’t lose it - immigration wanted to see it for my non-O application as well as for the extension application, despite the corresponding stamp in my passport. There was a moment of stress when I showed them the email with the circled check mark, which was inadequate - they needed to see the page that has the embassy seal in the header, and I had stapled it under the check mark page, so we skipped by it several times.