I remember seeing something similar some time ago in this thread but I gave this method a chance today: Wow! ZST fits like a glove now. My left ear canal is slightly smaller so I needed to adjust every time the fit otherwise it'd sound muffed/blocked but now fitting is excellent. Also, I've covered the nozzle with a damping material (silica gel bag fabric) and now 0 problems regarding sibilance. Oh.. Btw, I liked the result using Comply T-400 as @Francisk has suggested many times but the durability and price is a deal breaker for me (maybe because I've been using ZST as workout IEM) so I'll stick with this Sugru + damping solution.