Try these: keep it at 50ms (so it also says this in the top-left too), zoom in the camera, lure the npc so it's chasing you, get -65 magic defence bonus so you splash, put the alch item in the correct slot, disable spell filtering, and you'll get maximum exp/hr with these.
EDIT:
Here's a quick setup guide just in case anyone is wondering: (i'm doing curse which is lower xp vs. stuns)