Maybe I'm missing something embarrassingly basic, but I'm new to the forum and to the app, so bear with me please:

Years ago in my daily illustration work I used 'real' airbrushes. I now want to add both highlights and shadows to a vector shape (a heart) in order to produce a 3D appearance. I created the necessary vector curves and applied an airbrush style. After much digging I managed to find the transparency control and got close to the effect I'm after.

A problem I can't seem to overcome, however, is that the feathered/airbrushed lines are not completely smooth, but appear more like a series of blurred blobs - what I'd expect when using a real airbrush with insufficient air pressure, in fact. Wireframe view reveals a series of many ellipses along the path - something which surprised me, but might give someone else a clue as to where I'm going wrong. Assuming I'm going wrong.

So, any ideas or suggestions, please?