I have found this works great when the ear plug is split lengthwise in quarters. Halfs was just too big. Also seems to work best on bobs that are known to be very long to come to rest, such as TZ, TS, AFM, etc. I didn’t see too much difference on modern Stern tilt bobs.
I also noticed that to get the same sensitivity as without the ear plugs, I needed to move the bob up ever so slightly.