John Aniano in Central NJ
Having built only two sackback Windsor chairs, I may not be the best to comment, but...
I'm assuming you are using the adze for the initial hollowing of the seat. If you aren't making a lot of chairs, you might consider using only a good, sharp scorp to hollow out the seat. I have two gutter adzes and I probably used them for 2 minutes per seat. You are only hollowing out ~3/4" max, right? Spend 5 minutes and use the scorp, which has lots of control. I followed with a sharp compass plane. My travisher does work, but my compass plane gave a better finish, and was more intuitive for carving, at least for me...
Why when typing the word "scorp" does the software insist you mean to say "Scorpio"? Now that's a question that needs answering!