Mike, let me go at this from a different approach... With the Sierra pen design, the length of the tube/body can vary quite a bit (+-.125 at least) without any affect to the refill exposure. This is because the upper end of the refill mechanism can slide into the top cap of the pen, where it is grabbed by friction, and has NOTHING to do with the refill/tip exposure. Check for yourself - pull the top cap/body off the nib/tip, and you can twist the end of the retract mechanism and the refill tip extends/retracts.
What exactly makes you think the pen body is .030" too short? That should have NO effect on how far the refill tip is exposed.