It depends on the radius of the fretboard but I tend to go with about 2.4 mm from the top of the 17th fret to the underside of the E string and 2 mm on the G.
Never played an Octave Mando but have been intrigued by them for a while now.
I can't imagine that one at that price point would be decent quality but who knows? With their return policy being rather good, it might be worth a try.
Could well be a shielding problem.
If the buzz goes away when you touch the strings etc. then the bridge earth is probably good.
Make sure it's not something in the room, dimmer switches are notorious for this.
My home built gigging bass.
Fender Jap 62 reissue neck.
Squier body.
G&L MFD pick ups.
Babicz bridge.
Lightweight and an aggressive, growly beast of a bass.
[url="https://flic.kr/p/FBFMGn"][/url]