Is 3 Rivers spine calculator accurate

[Ray Johnson]

I'm shooting a Centaur Chimera that is 44#@28".I draw about 27".I am shooting a Beman Hunter .500 that is about 30.25" long with a 100gr brass insert and 175 gr fp.The bare shaft hits right with fletched arrows at 20 yards.The calculator shows that my arrow is way weak for the bow.Now,the only option for bow type was the Centaur carbon elite which is faster than the Chimera but that was my only choice.I am not changing anything based on the calculator alone but I was just wondering what y'all thought.Have any of you found the calculator to be off on your setup?Also,do y'all think the arrow I'm using should be right for my bow?