here on europa i do not experience any problems with the virtue/anni arties. in average it takes around 30-45 minutes in fel for one drop when farming and there is no special trick about it.
my experience is, better kill 1000's of low level mobs than hunting the biggies, for example, equip your lizardman slayer on your strong melee warrior and do rounds through despise lev 1. once your finished with one round, the mob definitely has respawned. too, you might end up near the entrance, so you could quickly walk the few steps outside, recall home to unload hides and gold and be right back for the next turn. if you get tired of stopping to loot, have a friend join to skin/loot the corpses while one of you slaughters the critters.
the higher level critters mostly live in crowded places, attracting the occasional red, so your danger of an encounter is reduced and your chance to dodge a possible attacker is increased when staying away from these "points of interest".
