Question re Aircraft Spawning

[wsuch 1]

Hi All

 

Coming back to this after several years but one thing I just cant get my head around is how inbound aircraft just materialise inside the boundary of the sector, for example I have an inbound jet at say 20 miles coming from the south and all of a sudden another jet will just instantly appear on radar in front of this plane at 10 miles going direct to a fix, very unrealistic as far as i can tell

 

Thanks

Wayne