I just wonder how easily activatable your new switch for the middle button is gonna feel compared to a main button switch with the same actuation force. When I was replacing my main button switches, it didn't go as I expected and the ease of actuation actually strongly depended on whether my fingers rested towards the front or the back of the mouse and from my understanding also the degree to which the clickers were bent towards the switch. Maybe even more so than what actuation force your switch has in some cases. So I was thinking maybe in the case of the middle button there may also be factors like that at play that lead to an unexpected result.