Real focal length and online focal length calculators

I got an sx50 and at the longest focal length which is 215mm the field of view 14ft from the lens was 17 cm horizontal but according to online calculators only 155mm is needed to get this field of view with 1/2.3 sensor. I checked several calculator   sites and checked those sites against canon's own calculator http://www.canon.com/bctv/calculator/calculator3.html

Why is there so much difference ?