Your last comment is very appropriate for cognitive and reading studies. A stream of communication does have certain time limits, or length limits. This should help the interpretive process, because the ancient author and audience had to process these things orally at some point. These letters were intended to be read outloud.Syntax remains important here because it helps directs how to put the pieces together. Many of the important signals for doing so are located at the left edge of these units, e.g., οὐκ ... οὐδὲ ... ἀλλά .... But there are places later on, especially the anacolutha in chapter 2, where the syntax is simply abandoned. There is no whole to construe syntactically, only a series of fall starts and rabbit trails. I would also suggest that syntax alone is not sufficient to grasp Eph 1:3-14, because the monstrosity is simply too big to keep entirely in one's active memory until the very end.
An author or audience have a certain small length of time, maybe 2 seconds, in which to encapsulate a reduced form of the message and hold it in memory for linking with other encapsulated pieces. If something doesn't get reduced into a storable unit piece, then everything collapses in short time. A person can experience this even in their mothertongue. Take an unread sentence in some text. Cover it before getting a glimpse of it. Then slowly uncover one word at a time while momentarily glancing anywhere, so that no more than one word is seen per second, without seeing the earlier words. After a few seconds the meaning is blank. If not, then the reader has been doing some secondary conscious memory work to overcome the meaning collapse.
This may help a reader today, since it can point out areas in Eph 1.3-14 where someone may have naturally read fairly fast to cover enough ground, and it will also focus on natural segmentations that an audience used to store the little piece-units of meaning that are strung together. It even ties into relevance theory because some "exegeses" might require too-high demands on processing.
this is also related to things like reading an underdifferentiated script like an unpointed Semitic language. there are times when one reads along a stream of words and gets to a point where it is obvious that one took the wrong fork in the road and one rereads the sentence.