You are correct to point out that if you send exactly 3.5999749793 XMR (3.6 XMR - e.g. 0.000025020730 XMR tx fee) to your recipient, by referencing 11 outputs in your ring signature, one of which is exactly 3.6 XMR, they will have a high chance of guessing that you are spending the mined output.
This, however, is a somewhat contrived example. Most of the time, you're not spending the exact amount of a particular output (minus the fee) you have in your wallet. If you'd sent someone 3.5 XMR, then they would be oblivious. Only when the amount you send is the exact amount of the output (minus the fee) can they make a decent guess.
In practice the only time that this scenario would happen is if you're sweeping your entire wallet contents to a third party. In that scenario, for there to be a threat, you'd need to have only ever received coinbase outputs to your wallet, and never have made a single transaction from that wallet that spent any fraction of those coinbase outputs. If this scenario is applicable to you, you can easily solve this problem by sweeping the contents of your wallet to yourself before transferring funds to a third party.
Also note that even if the above scenario applies, coinbase outputs can be some of the most anonymous outputs to own in the first place. This is because when you mine the output, if you conceal your IP address when submitting the successfully mined block to the network, then there is no record with e.g. an exchange that will associate that output with your real world identity. Therefore knowledge of that one-time output address being spent will reveal nothing of any value.
