im not up on all the skills for Rt/Me so cant think of a solution at the mo
*must do research*

it (whatever your farming) should be well and truely dead by then ... if it is'nt it should be very close, nothing that vengeful weapon wont fix 
. He does out dmg your khanhei when hes alone so lure him with at least 2 other groups of vermin, by the time the normal ones drop he should be very badly injured himself so now is the time to start stacking khanhei with vengeful weapon against him 
. He does out dmg your khanhei when hes alone so lure him with at least 2 other groups of vermin, by the time the normal ones drop he should be very badly injured himself so now is the time to start stacking khanhei with vengeful weapon against him