I’m 100% positive it will retard with rpm.
What I can’t say is when it starts and how much it will retard.
I have some videos of different boxes retarding on my YouTube page.
Baldwin Carbs has (at least he used to but I haven’t looked lately) some videos of the same thing.
That’s where I first learned of slew rate and such. That’s why I bought my own test bench. It can be so bad it’s no wonder guys can “upgrade” ignition systems and lose power. The retard certainly affects power.
@92b is going to do some testing when he gets a minute to do it. I’m waiting on his results. It should be interesting.
If you are down for the cause, you can send me your box, coil and distributor and I’ll test it for free as long as you pay the freight and I can make a video and post it to my channel.
Let me know.