Shift lights not representing ideal shift point for some cars

While I'm aware that shift lights cannot always tell you the perfect time for shifting up due to the car's power band or the situation you are in, in most cars they give you a pretty good guess as when to shift.
However, after testing and using external telemetry tools, I've noticed that the shift lights in some cars can be completely off, making you go considerably slower than what the car can actually achieve.
This is all given that the ideal shift point is usually marked by flashing lights, when the bar in the mini display turns red, and a few other ways.

I haven't tested all the cars in the game, but these cars have misleading shift lights:

• Both 2020 DTM cars: Shift at the first yellow light in cockpit, third green light (BMW) / fifth green light (Audi) on full data display, right after the bar passes the tyres on the mini display
• 2005 C-Klasse DTM: Shift when the red light appears in cockpit, first red light on full data display, when the bar turns green on the mini display
  
• Bentley Continental GT3 Evo: Shift at the second yellow light in cockpit, second blue light on full data display, when the bar is between the tyres and fuel on the mini display
• (...)

Like I said in the first paragraph, these points won't be the perfect shift points at all time but they will no doubt be better than what the game does on auto shifting and when the lights flash to warn the driver to shift up.
The telemetry isn't lying either. When I started shifting up at those points I had improved my lap times considerably, especially on the straights, and the horsepower readouts match the graph on the setup page.

Now for why I say these shifting points are better.
For maximum performance on straight lines you want to wander around the horsepower peak, that is when the engine is outputting the most acceleration. Oversimplified, I know.
Shift lights are used to tell the driver when to shift so they avoid hitting the rev limiter or staying on a less than ideal part of the engine's power band.
If you were to shift the cars listed above when the shift lights start flashing you'd be missing peak power or experiencing it for a much shorter time, resulting in less speed.
I don't know if this is intended, or if these cars are meant to be short shifted IRL for peak performance as well, but considering so many cars have their shifting points marked by flashing lights, sometimes even in the same class of car (like the Bentley), I'm lead to believe that something's off.

 

One for @Alex Hodgkinson

 

Thanks for the reply Alex!

I did find the thread about the BMW M4 GT4 and I believe the FR X-22 and M4 GT3 also tell you to shift before the 97.5% threshold.

I don't know the details about the real stuff, but I'd guess that the shift indicator always happens at the same RPM regardless of gear. At least this is the behavior other simulators and games have.
As you mentioned, different gears will drop different RPMs and many cars usually end up telling you to shift too early for lower gears and too late for higher gears, but I'd say that's up to the driver to analyze the data and see how to optimize the gear shifts to the maximum.

I just wanted to bring attention to some outliers where the shifting lights are really off and likely need special treatment like the cars mentioned in this reply.