I am currently playing a stealth sniper and I have two bonus sneak damage perks. One is maxed out Sandman which gives me +50% sneak damage and the other is level 2 Ninja which gives me x3 damage for sneak attacks. My question is mostly why it gives me a x4.5 multiplier instead of a x3.5. Is it because it is ((0.5*3)+3) or is it a bug?

Thanks!

Ninja is factored into the total damage before Sandman is. With Ninja you're getting a 3x multiplier, and with Sandman you're getting an additional 50% on top of that, so yes, you're getting 3+.5(3)=4.5xdamage

this is a good post. i almost ALWAYS play BoS. in a rare moment, i chose to do a stealth character too. i have been trying to make her a stealth melee, but i am finding it hard to sneak up close enough to make the attack, and get the bonuses mentioned, before i am noticed. so i have been gravitating towards a sniper too.

Stealth melee becomes easy once you get Sneak 2 and at least Level 1 of Blitz. And if you play at night and avoid lights. But till you invest in sneak perks shadowed and light leather armor works wonders, of course you need Armorer for that.