The efficiency of the original post was 75% so maybe you have a higher value?
Also depending on the software you are using and how you set it up you could be using a different IBU calculator than the original poster.
Normally either Tinseth or Rager.
Generally Rager attribute more IBUs to the bittering hops than Tinseth and it's the other way around for the additions in the last 30 mins i.e. Rager attributes more IBUs to the flavour aroma additions, relative to Tinseth.
Since the ratio of bitter hops to aroma/flavour is 1:1 and you are getting more IBUs I would guess that the OP was using Tinseth and that you were using Rager but it's all just guess work
Edited to add:
I also forgot the obvious one - did you adjust weight to match the alpha acid % of the OP?
If your hops have a higher value then you will get more IBUs and need to use less to get the same value.