As Stew says above, FOR CALCULATION PURPOSES, this is no doubt overkill. The reality is that in the shop, the fabricator will oversize to some degree based on fab methods. From a code standpoint, the formulas are inherently conservative, and again, the reality is that no engineer in their right mind would normally list 3.94" as a repad width on a fab drawing.
HOWEVER...
There ARE times when a vessel head is a very busy place, and trying to find a landing spot for a new bracket/ nozzle/whatever really does get to be a challenge. So I generally like to model repads as accurately as possible. They're a bit of a challenge, and there are several approaches. I've attached the method I like.
Todd
Product Design Collection (Inventor Pro, 3DSMax, HSMWorks)
Fusion 360 / Fusion Team