Hi Rachfan…. just a few thoughts…. In the fugue, there are tied notes in the lower voice in measures 5 and 6 … (you play them short… ) Also, along the same idea, in measure 6 in the upper voice on beat 4, the f is held to the first half beat of measure 7. In measure 9, there is a question and answer going on (not only with the upper voice which is then 'echoed' in the middle voice half way thru the measure…which you Do bring out) but Also with the first beat in the middle voice as the quarter note g, being answered by the e flat in the upper voice, quarter note on the 3rd beat…and that pattern continues into the next measure as well… You play these notes staccato…they should be held for their full value, and perhaps even slightly accented …in order to reveal 2 ping pong games going on at the same time…. As the piece continues, there are similar places with ties, or where one hand is to play 2 voices, while one voice is holding while the other is moving - as again in measure 22… This helps to bring out the polyphony… I do however know that you are aware of this idea, as you say: "or playing two different touches within the hand". … But in these places mentioned, you could employ that idea …and to great effect…. (To me, it makes the composition become almost 3 dimensional)… Also, as the tempo is a bit bumpy, you might play it at a slower speed…. I hope this response has been helpful.
Cheers!