True: different engines handle different solutions better or worse. There seems to be a trendline for general lay-outs of engines, but no rock-solid science yet.
One thing I dare say from experience, is that the lowest achievable idle on the ground is NOT the lowest achievable idle in the air.
It is possible to idle lower in the air (which makes landing easier in some cases) while still maintaining a 100% reliable throttle response. I am not sure how this works, but it is something I found to be invariably true.
So nowadays I do not sweat it if I cannot get a reliable idle below 3K, I try to get it as low as possible, and then I just go fly, and in the air trim the idle back to 2500 (just using the trim) which is low enough for any plane I know to land safely and comfortably.
On the ground, I keep the engine at 3K with the throttle. No big deal.
It is of course possible to link this raised idle to a switch, but switches can be forgotten after take off, and I prefer an engine that requires a bit attention on the ground over a plane that overshoots the runway due to a higher than expected idle.
After all, as Herr Uli Streich (of Vario Helicopters fame) once said: Carb settings on the starting table are irrelevant, carb settings in the air are all that matter. Now if a helicopter guy (most depending on a safe working engine in the entire aeronautical discipline) says that, then I tend to believe him...
