Extruded Cut with a curved surface

Hi all,

So with regards to the attached file...

I'm trying to use the sketch "SKETCH Cut Bot Extrude to cut through one side of the "Bottom Extrusion" part.

However, I've tried both Through All & a Blind cut (the latter with enough distance/depth), and all I get is the tool either removing everything or nothing at all.

Any help would be appreciated. Thanks in advance !

SolidworksModeling And Assemblies