Stone, I'm not an IR expert at all, and I've never shot the Rollei film (just HIE and Efke), but I think one of the differences you need to account for in your images is how the sun is lighting your subject. In the first instance it looks to be behind (or to the side) of the tree, and I think you want to avoid any backlighting with the sun in the frame. The tree and bushes look underexposed (for IR) which would could be the problem with the mushy grain (again, speaking from experience with other films, not this one). The "one from the car" is clearly front/side-lit from the sun and the grain looks nice and clean.
I've seen IR photos taken in tombs and underground locations, foggy weather, etc. -- as long as there is some source of infrared light, you can get an IR shot -- and although it will be grainy, that can lend itself to the atmosphere of the photo -- just depends on the subject. If and when you test your film, remember to do it in a variety of lighting conditions, and preferably at different times of day, so can see what you prefer in your IR shots.