Does the target emission raduis effect the IBL when using a HDRI image?
Or when using IBL the only setting i need to control is the intensity of the HDRI map?
Also, the texture resolution and adaptiveness, how do these parametres affect the IBL? I have a HDRI map that is 4000 x 3000 pixels. what is the best texture resolution to use? Does the resolution affact render times?
I have not tested how much res affects render times, but I believe it does. For sure it affects the image quality for visible reflections of the dome. I think Vraylights are very well optimized though, so the speed hit is probably not so bad that it’s worth using sIBL type approaches. YMMV. As a rule I set the resolution of the light texture to match the image - so 4K in your case. I leave adaptiveness at default.
Target radius is, I think, for photons so the effect depends on GI and caustic settings. I use BF/LC for almost everything and never touch that parameter.
How can you make the resolution go above 2048?
Thanks for the info, that clears it up for me 
although I am interested to know why it doesn’t go above 2048 also.
It will only matter if you use photon mapping for GI and/or caustics and then, only for those effects. It won’t affect regular direct lighting.
Best regards,
Vlado
The resolution and the adaptiveness affect the way shadow rays are generated towards bright portions of the map. Increasing the resolution takes more RAM and slightly slows down the render times, but will make the adaptation to follow more closely the light intensity. It’s probably not necessary to try and match the resolution completely; most of the time even an approximation works very well.
Best regards,
Vlado
Maybe I never have :). Cant say I noticed that actually… Guess it just hasn’t been an issue.
Actually, I remember a thread specifically about this and vlado added some input.
Found it.
well there you go then - moot point 
Thanks for the link.
b