So my question to all of you is: Could it actually be possible that it doesn't really matter if you select engine anti ice at +10 or +6? Or is there actually a difference between different engine types and how prone they are to icing?
Yes!!!
But the differences are more in the damage than in the onset of icing. Either way, the concern is that the pilots start thinking that, hey, I never had any problems before so it must be allright. Or that it's a Boeing vs an Airbus, or more likely a GE vs a Pratt or Rolls. What they have no way of knowing are the subtle variations in the sub modules and installations that make the real difference.
Not wanting any crashes period, no matter who was the manufacturer, they simply recommend the 10C as the "safe number"
Now if the manufacturers should find that they are being out-guessed by people without the real design knowledge, this will just encourage the Feds to step in and mandate a rule change (hint, hint)