Speaker spacing and listening distance are directly related. 3.8 m apart is theoretically spot on if you sit something around 3.8m from each speaker (3.2m from the centre point between them), but would likely be excessively wide if you sit only 2m away, and too close if you sit 6m away…
Thare are several threads giving guidance as to how to optimise speaker and listening positions. this one has perhaps more info than most: Don’t forget this thread: Speaker placement guide which contains other guidance on speaker positioning (and given the real world differences between rooms, not just their dimensions, all guidance can only be a starting point.
Of course, in reality the various guides can only be just that because every room is different, everything in it having an effect as well as shape, how the room is constructed, and characteristics of the music system. In effect they can give you a starting point (and different tools may give different starting points,). Then you can start to optimise. Some people optimise by ear, but I find REW is a far quicker way, as testing each position takes only a minute of so, and can be compared directly with previous without having to go back and forth a cocuo,e of times to verify. REW is free software, though it needs a measuring microphone (more info if you search this forum).