There are issues that I have with the eye detect AF on my R6 while using the RF 100-500mm too. While the eye detect AF is great, it's not perfect. Let me reword that, there are a lot of imperfect situations where the eye detect can fail and the AF misses the mark. As an example, if the eye detect locks on to a woodpecker clinging to the side of a tree and the woodpecker turns its head and AF loses sight of the eye, you could find your AF suddenly going up and down the front of the tree while the AF searches the closest object looking for an eye. Any shots you might have been taking at the time would be on the soft side. I speak from a bit of experience of taking some really sharp photos of one particular woodpecker friendly tree trunk. That's just one situation where eye detect can be frustrating. It's a great tool, but it's not a, 'One Tool Does All', kind of tool. I highly recommend using two back buttons for focusing on any camera that allows it, it makes working with/without the eye detect a lot easier for me.