Given that changes in landscapes change over time, there is often a lack of distinctive permanent structures (like rock formations) present at locations, as well as the imprecisions of human memory processing which becomes more evident as time elapses, believe it is not uncommon for later monuments depicting a specific past event to be placed in approximate, rather than exact locations, of where it happened. Some latter-day monuments have also been known to be placed at sites convenient for modern visitors to access, even if it meant sacrificing a degree of historical accuracy. (For example, believe the monument to Smith's Independent NY Battery was placed at Devil's Den, not at its true battlefield position on Houck's Ridge, for better visibility to visitors)
Don't think the subject spot highlighted in this thread is an isolated case. Because of the reasons above, have little doubt that many instances can be found of monuments situate in locations that do not accurately record the spot of the actual event (e.g. the monument showing where Reynolds was mortally wounded in the Herbst Woods, at Gettysburg).
Bringing the