Monetized My Newsletter (Kinda)

I have an archaeological/anthropological newsletter that has nearly 1200 subs with a ~50% open rate, and I just monetized it over the weekend. I got a couple of upgrades to the paid tier right away (including some yearly plans), so I had high hopes. Now, a few days later, I have a total of 12 paid subs. That's a pretty terrible conversion rate.

Current setup is: Free tier gets top 5 archaeological headlines every week curated and summarized. Paid tier ($8/mo) gets all (20-30) archaeological headlines every week curated and summarized, plus recommended content.

I plan to ad sponsors to the free tier eventually so that'll help. But now I've gotta figure out whether to change how the tiers are structured, or just keep going and let it grow over time.

Thoughts welcome :)