A couple of things to keep in mind about mining fees:

  • Mining fees are computed per the physical size of the transaction (in bytes), rather than the transaction amount (in BTC). This is because transactions with a larger byte size (generally the result of having multiple unspents used as inputs for the transaction) are more difficult to mine. This is why comparing the fees as a percentage of the transaction amount is not accurate.
  • Mining fee rates vary according to overall transaction volume in the blockchain. When transaction activity is relatively low, so are mining fees. But as transaction activity increases, mining fee rates will also increase.

To illustrate this second point, take a look at this link, which tracks transaction activity over the past 30 days:https://jochen-hoenicke.de/queue/#30d

Now, take a look at this link, which shows how average mining fees change as transaction activity changes: https://p2sh.info/dashboard/db/fee-estimation?orgId=1&from=now-30d&to=now