What kind of range do you need to solo bosses?

Zakum should be fine for you but a list of your equips and % boss damage would help too since bosses like regular HT and PB would be easier if you can kill much faster or have good status resist.

I am admittedly curious too since I'm now at what I'd consider a rather high range. Sadly I'm only at 16% boss and have no Hero's Will yet.