What did your government do after a "counterfeited" Iranian passport was detected on an Indian intelligence operative? First off, the fencing on the Iranian border is not complete, even when it would be, there would still be infiltration considering the fencing is not a hi-tech sensor laid smart fence. Tunnels could be made under the fence to move men and materials. Israel with all its technological might still gets infiltration from Gaza every now and then. All it takes from insurgents is a determination to circumvent these obstacles. PS. no one claimed that the entire BLF cadre is based out of Iran (strawman logical fallacy). Iran is, however, a sanctuary for its leadership cadre and a place where foot soldiers can fall back to when the going gets tough.
FYI, even Iraq sponsored militancy in Balochistan during the '70s. Did Iraq share a border with Pakistan? My expectations are based on empirical evidence and knowledge of my own nation's history.