problems related to SC guide

[eggpain24]

I got some doubts about the adverbial modifier when I see this example in the "Place Your Words" session.

ALL the children are covered in mud. (emphasize the number)
The children are ALL covered in mud. (emphasize the degree of mud covering)

From the sample above, I just wonder that is it always true for this kind of adverbial modifier modifying the element after it?

If that understanding were true, then how could I explain the meaning difference of the sentence written below?

seismic waves most quickly travel through quick regions.
seismic waves travel most quickly through cold regions.

[eggpain24]

is there any instructor？