go to this dir

\Program Files\Jane's Combat Simulations\USAF\Resource\3DObjects\CoverElements

you'll see 4 dirs 1 for each terrain in each of these you'll find an ini file ( TCoverLasVegas.ini for example ) open with notepad and find the section below

[Ranges]
MinRadius=1200
MaxRadius=2000
MinDensity=80
MaxDensity=200

Change the MinDensity and MaxDensity values , add comment lines with the original values so you can change back , see example below

[Ranges]
MinRadius=1200
MaxRadius=2000
MinDensity=800
;was 80
MaxDensity=2000
;was 200

then save your changed file

You'll get more trees rocks etc.

Not much use but I thought I'd post it anyway