One way is scatter terrain. Modules gives the impression of large things you have to work your way around, when often the figures should be embedded in the terrain. Branches, low rocks, termite mounds etc help to provide light cover.
3D base board - dry river beds for models to use as cover, or to move without being spotted. Hills work the same way - easy to climb over but disrupt line of sight.
"modules" of terrain that provide lighter cover but encourage figures to get in. A circle of rocks to set up a command post, or a stand of elephant grass to hide in.
Real-world jungle boards often have a mix of terrain - trails, roads, villages, paddy fields, swamps, waterfalls.
Dense, virgin jungle should be hell to live in, move through and fight in. Humid and hot, no lines of sight, your equipment rusting and clothes rotting off your body, rashes and bugs. You can find yourself walking on a "mat of branches 20ft above the forest floor without even realising it. And all that's before you meet the local wildlife...
Nice report, by the way!