Drops and number of monsters

I heard somewhere that if you kill all enemies in one big group you get less drops. Is this true?

For example, I'm farming UW and I see 2 groups of 3 smite crawlers, will I have a better chance to get an ecto if I kill the group one at a time or will it not matter at all If I aggro both groups and kill them all?

There are a couple of points here.

There have been several threads on these forums (mainly in the Farming section) suggesting that killing monsters slower results in more drops.

My own personal experience also supports this theory, but I doubt that we will ever really know, as ANet tend to keep these things secret.

However, rare materials including ectos are exempt from loot scaling, so in this case I doubt that it will make any difference.

You may possibly see more low level white/purple and gold coin drops if you farm slower though.

Try a few runs slowly and a few runs fast and see which one you feel gives you the best results.

A lot depends on what method you enjoy playing most too.

Yes. The frequency of Loot-scaled drops is limited. Kill everything at once - not many drops. Kill things slowly, one at a time - a lot more drops overall. This has been practically confirmed experimentally for a while now.

This is the infamous "Anti-Nuke Code" everyone has been complaining about, and was introduced as part of the Hard Mode update along with the rest of loot scaling.

Non Loot-scaled drops don't appear to be affected by this (rares etc) so your ectos should be safe.

i think it works like this if u can kill evey thing at once the drop rate for rares are up some %.. and if u kill one at a time mostly likely get a white or bule. thats what i think

Yes but because killing them separately takes longer, your income rates with the two methods should be fairly similar.
Not sure whether this bit of programming falls under lootscaling or not.