When a empty monster dies It can drop 3 memory related items, going to use a Fire core as an example. Weeper Fire core max drop would be Burning mem. (fire), Radiant mem.(light) and a Recollection used in the BCs. They can drop 1 memory for their element, and 1 for what their element is a part of Light or Dark. For light or Dark core empties this makes it just drop 2 of the same type. As 99 thf w/ TH8 on average I'll get a drop about 40% of the times, and it is normally just 1 item, it's not uncommon for me to kill 4 or 5 fire cores in a row and get no drops, when I do get a drop it seems split 40% burning, 40% radiant, 20% recollection. So killing 5 fire cores I could walk away with 5 radiant and no burning, the rate at which I'll see double drops is off too, it is more common to see a Memory and a recollection drop than 2 Memories.
I know that the higher lvl you are above the monster the lower the drop rate and the Idle empties will give exp to a 99, but the problem with them is they don't have a set core. killing an Idle weeper can got you nothing or a random element, you cant tell by looking at them what you'll get, and even then the drop rate isn't any better.
I have 1 request, it's not boost the drop rate or make them drop memories at 100%. My request is simply make a Empty drop 2 of it core instead of 1 core and 1 light or dark. So if I Kill a Fire core it should have a chance to drop 2 burning instead of 1 burning and 1 radiant. Light and Dark core aren't even rare they spawn at the same rate as the rest, so why flood people with those memories when they are only after certain ones.