well, I've been soloing in mostly a very restricted list of areas these last few months. Abyssea, Sky (flamingo/sprinkler/Groundskeeper pages, did a few runs of aura butlers for GoV out of curiosity), Misereaux coast/Riverne (Seaboard vultures, Darners), B. Tree (mourioche/rabbits and korrigan/elder goobbue pages) and campaign. The focus has been on getting certain jobs from 90 to 99, merits, and skilling up weapons and things like magics, guard, shield, and parry with level appropriate targets to the skills. Got a couple avatarites off the groundskeepers early on with SAM, was still only 91 because I had just finished the kill list for WS trial and hadn't dinged again yet (was shooting for ranged skills and hoping for some odd parry as I had luck with it there in the past). Since then, I've been going with the assumption it's targets over 75, which also seemed to fit with me getting them off the Canyon Scorpion (91 MNK, Solo, WS trial) and Shadow lizards since their levels start right around 75 and was getting avatarites off them when using them for trials.
In this case with DRK, I've been doing almost exclusively Campaign/besieged/abyssea and just the other day I hit the wivre after a Grauberg campaign battle ended abrubtly while I was getting tags. Wind was up and I didn't want to leave empty handed--it was the ones right there at the fort. Forget what level I was (levels fly by at 9k+ a campaign and 15k per besieged), think I was getting 40 a kill from them. Got one of each on back to back kills and was shocked because I knew they were such a low level, even commented on it in LS chat because it didn't seem right.
As for what is reported at wiki, they still have verification tags up....probly because not enough data has been gathered for enough confidence to lock it in yet. The same thing happened when KC's were added. Everyone started high and then we found they dropped from lower level mobs as time went on. This could be the case here as well, it's just such a rare rate that the sample may not be showing the bottom level just yet. Killed roughly 220 shadow lizards last week for a friend's trial across two runs on firesdays (@94 DRK or so, Fell Cleaving with others) and we only got 3 Ifritites to drop--not a large sample set, but in the scope of those kills that is just barely past 1.3%, and that was a kill rate of better than 100/hr, so it was a steady stream of rolls for them to drop from. Even when we did the first 100 in a short slaughterfest on Dusk Lizrds (on SAM with Tachi: Shoha, spawns are 83+, capped azure and started TE's in about 20 minutes by popping the NM a few times too) and I stayed in there soloing for almost 3 hours after, I only walked out with a handful of avatarites. They simply have a crappy drop rate some times (well, most the time if no weather). So it may very well take a while to get a complete sample set on just where the cutoff is. Maybe it's level diff, maybe it's not. Hard to test for that when the people testing it are capped levels (or at least 90). Who knows for certain without something specific from SE on the issue or more reports from 70-somethings coming up outside abyssea to provide a more diverse result set.
DRK hit 99 and just needs skills topped off now, so I'll be switching to WAR soon and will be doing trials on that as well--possibly in some lower level areas as well. Maybe I'll see it happen again, who knows. If it does, will be spreading the word.