The simplest answer is that present perfect always refers to an interval of time ending at the present time, not before. It never refers to a simple point in time, to a time interval that ended before the present, or to a time interval any part of which is still in the future.
For example, in the sentence "I have been at home since 3:00 PM", the present perfect makes "since 3:00 PM" equivalent to "from 3:00 PM until now".
Present perfect does not imply that an action or state necessarily fills the time interval referred to. "I have been at home since 3:00 PM" could mean either "I have been at home ever since 3:00 PM" (for the entire time from 3:00 PM until now) or "I have been at home at least once since 3:00 PM" (one or more times during that time interval).
"I have not been at home since 3:00 PM" means the opposite of either interpretation of "I have been at home since 3:00 PM", but it still refers to (reports on) the same time interval.
Sometimes present perfect may suggest something about the present itself, but that has to be based on context and is not inherent in the use of present perfect.