The film is loosely based on the Niland Brothers. Two had been killed in Action on 6 and 7 Jun 44, and a third one was thought to have been killed when his B-25 Mitchell bomber was shot down in Burma (he actually parachuted out safely, but was captured by the Japanese).
"Fritz" Niland (H company 2/501 PIR, 101st A/B Div) actually DID wander over to the 82nd to visit his brother Bob. When it was discovered that all his other brothers were (presumed) to have been KIA, he was shipped back to the states to a non-combat job. (And flagged as "Non-Deployable".)
https://en.wikipedia.org/wiki/Niland_brothersSo apparently there was some "Wandering Around" in Normandy after D-Day. Especially among the Airborne troops (because they had been widely scattered).
And yes, the Germans might have setup the Machine bunker in front of the Radar Station. And yes, there were probably several more nearby (unmanned), and those Germans in the bunker were probably happy as hell, that no one had ordered them to the beaches. (Or if he had, was either being too dead or too busy to remember a couple of clown he had tasked with digging bunker(s) around radar installation that had gotten the *expletive deleted*it bombed out it.
But I do agree that IF (and that's a big IF) CPT Miller had assaulted and taken the bunker, that no prisoners would have taken. That's just part of the nature of taking out a MG nest or bunker. (Grenades are bad ju-ju in enclosed spaces.)
And yes, even I when watching the movie had qualms with bunker scene; 1) It's not part of your mission, 2) Why is the medic part of the assault? 3) Why not just bypass the strong point. The Germans failed to remove their "calling card" (the dead American soldiers), so they would still be there when the next batch of Americans arrived. They would see the same thing and perhaps have more folks to, 4) PROPERLY ASSAULT the bunker, like from behind. After doing a bit more reconnaissance, so see if they are stand-alone or part of a larger system. It's not like we needed to punch a hole in the German defensive network and this is the best place to do it.
Along with Upham not doing anything when the former prisoner was stabbing his buddy in the chest. I found that hard to believe.
And yes, shortly after D-Day, the Rangers were relieved of front line duties be reserve forces. Used where needed to help hold the line(s) especially at night.