Understand the fact that fees are not constant because of what we refer to as average congestions. The average fees fluctuate as more people broadcast transactions and use higher fees plus the higher the density of transactions on the network the higher the depth your transaction is placed. So the position of your transaction also determine how fast it'll get confirmed.
Also take note that your number of UTXOs required to pay for your transaction also contributes to how much you will pay in fees because of the fee rate and space the transaction will occupy in that block.
Users need to understand that this are fee rates that changes as more and more transactions are been paid with higher transaction fee, you might actually use a fee rate that will simply increase beyond that due to how other transactions paid higher and this is one reason why i usually advise people to pay slightly above the high priority if they are in haste to get their transactions included in the next available block. For example if high priority fee rate is 1sat/vbyte I usually go for 1.5sats/vByte to make it more preferable by miners for selection although not all wallets actually allows adding decimals
In cases though while you’re not in haste for fast transaction confirmation it is usually suitable to set medium or even low priority fee rate but the transaction in both case should be RBF enabled so you can Increase the fee later when the need arises