Irradiance map settings for huge image

I’m doing a 15000 x 9000 render of an interior with vray 1.5, and I’m wondering how to scale up the min/max limits on the image. -3/-1 is working great at 1600x900. LC is in world units so no worries there.

Here in this Tutorial from Flipside:

is the Info: “since we increased the resolution twice, we can decrease the irradiance map Min and Max rate by 2.”

400x325 = -1 -3
1600x1300 = -3 -5

And in the VRay-Help:

“Note that the presets are targeted for a typical 640x480 image. Larger images usually can do with lower Min/Max rates than those specified in the presets.”

something around -5 -7 or -6 -8…

to keep the imap resolution equivalent, every time you double the resolution, you can knock 1 off the min and max settings.

however a higher resolution image could benefit from more detailed lighting, so maybe dont decrease the max rate so much.

id probably (very roughly, not seen your scene) go for a nice low min rate, maybe -10 or even -12, then keep the max rate at say -3, or even -2 if you can swallow the calc times.