Timing Curve

Yes that is what YR and I are both saying.

Can be very annoying. Around 2007 was having this part throttle ping issue. Current engine, torque converter etc. Coming back from St Mary's City in eastern Md. which is about as flat as it gets, with a light rain, really couldn't ask for better conditions to suppress knock. Maybe an hour or two into the drive it was gurgling on every slight upslope or gentle passing of slow drivers. This was all US and state routes too - not interstate.
Looking back at my notes here that was
25* at 1500 rpm
28* at 2000 rpm
30* at 2200 rpm
30* at 2400 rpm up

Even taking two degrees out, it would still sometimes knock at part throttle. Even at an autocross where the engine is not nearly heat soaked.
I'ld have to dig deeper to get the vacuum advance info that went with that. But the point if using vacuum advance for what its intended - part throttle lower density fuel mixtures - then this is the rpm range where its easy to have too much mechanical timing.
It is possible to adjust when the vacuum advance starts as well as its limits. But I think its better to get the mechanical advance a little slower before messing with the vacuum advance.