Ziggomatic
500+ Head-Fier
I'd read about some people having possible fit issues and/or complaining about peaky trebles with the FLC8S. @Tranman409 recently posted a great suggestion about a new dual-flange SpinFit tip on the SE846 thread. This is the link to the medium size, but they also come in S and L:
https://www.amazon.com/gp/product/B06VVRXHG1
They roll off the treble just slightly (perhaps somewhere in between that of foam and regular SpinFits), which isn't necessarily ideal for the SE846, but for the FLC8S, it might be perfect for somebody wanting a bit less upper end than that from regular SpinFit or other single-flange silicone tips. They're also really comfortable and isolate really well (much better than regular SpinFits). They're expensive, but well worth checking out, especially for anybody who's currently struggling to get a good fit, seal or sound.
Ordered these on your advice, and, after listening for an hour, I agree with what you said about them 100%. Thanks for the rec.