Faction hits depend on the mob, level doesn't matter. If you're trying to raise faction, the vast majority of trash mobs give +1 point of faction whether they con green or red. So if you're just working faction and don't care about xp or loot, your work will go faster killing lower level mobs. However, various named mobs can give more faction such as +10 or +100 or "a lot".
Killing mobs lowers some factions and raises others, and you usually (always?) lose more on the lowered factions than you gain on the raised ones.
EQ doesn't give us exact faction numbers, but they can be determined indirectly which I have learned a lot about in the game.
thru -751 = ready to attack
-750 thru -501 = threateningly
-500 thru -101 = dubiously
-100 thru -1 = apprehensively
0 thru 99 = indifferently
100 thru 499 = amiably
500 thru 749 = kindly
750 thru 1099 = warmly
1100 and up = ally
As you can see, the number of kills it takes to raise faction a rank varies from one rank to the next. The apprehensive and indifferent ranks have the smallest range.
Your default base for all factions is 0 (indifferent) but will often be adjusted depending on what the mob or NPC thinks of your race, class, and/or religion. Mobs that hate all player races might give everyone a -1000 point adjustment with their faction, putting them in the "ready to attack" rank. Your home city's class guild will often give you a +100 adjustment, giving you amiable faction with them.
Doing faction work, you can gain or lose up to 2000 points from your starting faction, then you'll get a message that your faction standing could not possibly get any better or worse.