Weird - Forest looks completely different when rendered at different demensions

[stayinwonderland]

Need help trouble-shooting this. My grass gets brighter as I render larger images.

 

 

 

Not sure if this is a Vray setting or Forest setting. Rendered at 1000px, 2000px (and reduced down for the sake of comparison to 1k), ditto 4000px.

 

If it's Vray, it's got to be something that somehow relates to resolution. Even if you're not intimately familiar with Forest Pro, maybe someone could help trouble shooting it in a general sense?

 

Edit: some ideas... foliage uses vray 2 sided (just in case that does anything) I suspect that the larger resolutions are the truer representations of what's actually going on. Even though the lower res images look better. So the issue may be occurring at lower res than higher res.

Edited December 12, 2015 by stayinwonderland