Here is how to get the results you are looking for using the "Cut-Extrude" "Offset From Surface" command
Select the sketch you want to use to make the cut and in the features ribbon select Extruded Cut.
For this example, the from will be the sketch plane and for direction 1 we will choose "Offset from Surface"
Now we select the angled surface on the opposite side of the solid. (the surface has to cover the entire sketch so with more complex geometry you may need to play around with this)
And the distention of the offset is set just below (1.5)
Click the green check box and our cut is made. Lets get a section view to see how this looks.
select the appropriate cut plane
And here are the results.