Coral placement is as crucial to success with a captive coral reef as any parameter or piece of equiptment.  Mistakes can be made when building the reef that will inhibit growth and success as time passes and the specimens grow.  Placing Acropora corals in close proximity is safe in most instances as they do not have a strong mechanism to compete for space.  A soft coral or a stone coral such as Euphilia can however create a silent warfare that will inhibit growth and eventually cause death.  Often times as the corals grow and space becomes the limiting factor death will occur quite quickly.  The death can be misdiagnosed as one of the many other factors that are involved and add even more questions to the issue.  Experience with placement is a hard learned lesson and will undoubtedly confuse many.  Taking the time and patience to provide plenty of space when dealing with a mixed biotype style reef is essential for long term success.  A good rule to follow is to keep Acropora and Montipora species well away from soft corals and the large polyp stoney corals as this is where many of the issues occur.  Many of the Montipoas will get along nicely with Acropora specimens and that grown-in look can be realized if the time and dedication is provided.