Hey, last few days I did calculation sheet with a lot of engineer skills to calculate its damage in regard to your statistics. After doing all formulas I checked if its same tooltip damage in game as my calculations. After some time I managed to find correct formulas for most of skills but not for Refraction Cutter. As wiki says its CoE should be 1,1 (Link to wiki). Im pretty sure that tooltip damage is 1,0 value. I have no testing done in checking which value is used by skill in game, but in wiki patch notes you can notice that 1,0 was buffed to 1,1 long time ago. Did they forgot to update just tooltip damage or skill damage? I also tried looking for forum post with skill name to find patch notes undocumented on wiki but failed.
You can check by yourself by taking calculator and input A * B * C / D where
A is weapon strentgh (use 1000 if you have ascended sword)
B is your power (check in hero tab - "H" button)
C is skill CoE (here should be 1,1)
D is target armor (2597 is used for tooltip damge)
Here is (Link to wiki) with source for that.
Result will be higher then tooltip damage if you divide result with C (1,1) you will calculate formula for (1,0) and this will meet your tooltip damage.