I read a paperback novel in 1999 when I was suffering from pneumonia. My mother had purchased it from a thrift store for me, so it could have been from the 70s or 80s.
In this story, a squad of space deployable infantry is trapped on a planet (I believe it was a transport crash landing - I do not recall if their ship was attacked or had mechanical failure) , and is being observed or hunted by a small group alien beings as well as fighting off the alien wildlife. This planet has jungle and river areas. I believe that the group of infantry were attempting to reach a rescue zone or pickup point, or some high ground for a transporter.
I distinctly remember the following points:
One of the infantrymen describes a squad machine gun, telling the reader that this particular model of machine gun is nicknamed "The Hose", similar to the way an M60 machine gun is nicknamed "The Pig".
The aliens observing the infantry may not be totally adversarial in nature. In the epilogue, I believe one of them is discussing the interactions and what they have learned about the humans in a positive way. The terms that humans "contingency planning", "emergency procedures", and "grid navigational system" are great achievements or positive attributes for a "potential alliance".
The planet may have been in a "restricted area" or "off-limits space".
A sequence described the navigational methods of mapping space (the three-dimensional grid system mentioned at least three times), and lightly described the method of FTL travel in this universe.
I've scoured the internet with a few key words, but the title of this book eludes me. It is not the StarFist series. The feeling I get is that this book was published in the 80s.