It’s the nature of the electronics. It’s called slew rate.
An HEI will also retard. Anything that has electronics will have a slew rate.
Even your timing light has a slew rate. And they don’t all read the same. That’s why when doing a tune up I have the owner use their own timing light. That way if there is discrepancies between what the timing lights read they are already have the light they will be using.