First let me mention, that presets bundled with Forest Pack are "LWF ready", so there shouldn't be any gamma issue on commented set-up.
I'm afraid, that there are no "universal settings" as the final look depends mainly on the lightning set-up (in your case mainly on used HDRi map). Please double check if your scene is not slightly overexposed. The scene used for thumbnails renders has really simple set-up (similar to yours one): a VRayLight
type) with a VRayHDRI
Feel free to get inspired by settings mentioned for example on http://www.peterguthrie.net/blog/
, where you can find a lot of useful informations.
Attaching render of the "Common grass 01 (detail)" preset using the freely available "BBB3 Vray Mat Scene
" without changes.
To tweak the final look of the preset I would suggest you to add a Color Correction
map(s) and adjust it in a desired way.