Hey, the title says top dead center, it doesn't say about compression stroke. But the hint was to find the top of the compression stroke.
Thanks, pardner! I never thought of that.

There are two things one might want to check:
1. Where is TDC? (is my harmonic damper and pointer correct?).
2. What stroke am I on? (top of exhaust stroke or top of compression stroke?).

The OP's trick was good for #2. The piston stop method was good for #1.
I don't worry about what if the plastic plug sucked in because it'll burn up sooner or later. Same with the little paper ball. We don't always turn the engine over with the cam, lifters, pushrods and rockers installed. I've had my finger sucked partway into the spark plug hole. The whistle is nice but I have never seen one in a store.

OP, the occasional snarky reply is what you pay for being in on this outstanding accumulation of wisdom.

R.