@Kraco: There's a heavy armour perk that affects weapons? I'm assuming you're talking about having good Glass smithing so your glass weapons are improved heaps?

@Ani: It may be because I have not improved any of my armour at a forge at all. Might actually give that a go.. though I've essentially got no smithing abilities. I always assumed that in this game there are always at least two ways around obtaining something:

1) Find it.
2) Make it.
3) Buy it.

I finally found out why my Shadow Warrior attacks don't always get the sneak bonus when I've got allies nearby..

the key to a successful sneak attack actually is if your target is OUT of combat, so even if you are invisible for a brief time you will not back-stab targets that are let's say in combat with a companion or another NPC. It took me some time to figure out but yeah, if you want to be a stealth user, you have to play solo!