Imp streamline is not a good pve pick and actually screws you up because you drop aimed cast time too far below the global floor to cast explosive after aimed and take advantage of the talent. This is different in PvP because imp sl and tensile bowstring have PvP nerfs, but also explosive shot is really bad in PvP.
You want to queue it up after aimed shot such that it lands just before the aimed you just casted lands. If you have salvo volley, you can precast salvo volley then aimed → explosive and all of your explosive shots will get the buff. If you have a lnl proc and 4 set, you can salvo volley->explosive->use proc and then you get even more multipliers. Not sure if it’s been fixed since ptr but the 4 set was at one time buffing all of the impacted explosive shots in this scenario.