DL Yetis are great from 38-44 but at 45 they are mainly green. I went over to Eastern Wastes and would quad the ogre mercs, a group of 3 spawn and you can easily grab a roamer as the fourth. Decent xp and +10 CoV faction per kill.
#2 on the map
https://wiki.project1999.com/Eastern_Wastes
Once you can click the lumi 46-51 flies by in TD