Spine Calculator Question

[adudeuknow]

This is in regards to the spine calculator on 3rivers archery page.

i have used this and have had it really work amazingly for me in the past but as it stands right now i am shooting
#50 @ 28 with a 30inch draw...actual weight is around #55.5 on scale at 30"

arrows: easton traditional 340's left at full length of 32"
75 grain insert
200 grain field point or
190 tuffhead meathead


i bare shafted this combo with perfectly straight flight.

according to them my number should be 78.9 but my actual number is 45.

how can you explain my perfect arrow flight in regards to what this chart is telling me?

[adudeuknow]

i know sometimes you have just got to go with what works but i am curious as to why this has worked so well in the past and now the discrepancy seems to be too great to even be fathomable.