10mag - I have tried lower & higher mag but find 10 mag a great compromise for target magnification V target blur, for my taste anyway.
Around 23y parallax - I try & set my scope to just start to blur out about 15+, gives me a heads up for range, if its a 15mm very blurred I know its 13. I also (used to, as I don't shoot enough at moment) get used to blur at longer ranges to use as an range indicator, I don't use this as a main way to range but as one of afew aids I use as a whole.
I also use these settings for shooting SFT & back when I used to be able to shoot I would get around 25 targets (on a good day) on a FT course. Same again 10 mag a great compromise (for me) & the 23y parallax is blinking blurry but with a bit of practice it can be helpful (why I don't change PX, like you can in SFT, is another story)