There a couple of misconceptions here. The first is about reduced participial phrases. Generally this means transforming a clause, which has a finite verb, into a phrase with a non-finite verb. Thus
I came to work today while I was wearing my new suit
becomes
I came to work today, wearing my new suit
Secondly, I don't know what grammar is telling you that participial phrases have to modify adjectives. Participial phrases may act as modifiers for any construct that can take a modifier.
Next, I'm not sure what you think a "participial prepositional phrase" is. One example you give is
- This is good result(,) given how other teams performed
but there isn't a preposition in sight.
Participles by themselves don't really carry tense. You seem to think there's a difference in punctuation based on whether there's a present participle (one that ends in -ing, e.g., "coming home") or a present perfect participle (one that combines having with the plain form of the verb, e.g, "having come home"). There isn't.
Most of your examples may be parsed as nominative absolutes. For example,
I came to work today, wearing my new suit.
These aren't really restrictive or non-restrictive because they are independent of the grammar of the main clause (thus the name absolute). The wearing of the new suit applies not just to the subject, verb, or prepositional complement individually. The style manual I use, the Chicago Manual of Style recommends setting off introductory elements like this with a comma. CMOS also recommends setting off following non-restrictive elements with a comma, so I infer the same for following absolutes.
Punctuation is a matter of style, not grammar. So follow the rules in the manual of style that you've chosen or that has been thrust upon you.
Best Answer
The primary difference in the forms of the two sentences is that the first one has "eats... reading..." and the second one has "was making... talking..." It thus seems that the first sentence—punctuation aside—can be read only as signifying
whereas the second sentence—again, ignoring punctuation—can be read as meaning either
or
So perhaps the comma is there to signal a dropped and and to emphasize the parallelism between "making sandwiches" and "talking with her daughter," both of which attach to the word was if an implied and is at work. I certainly don't see the argument for putting a comma after "sandwiches" in the second sentence as being any stronger than the argument for putting one after "breakfast" in the first, if the point is simply to mark the absence of the intended word while in both cases.
Still, I'm at a disadvantage in trying to work out the book's reasoning because my preference would be to include the missing while in the first sentence and the missing while or and in the second sentence—and if you do those things, neither sentence needs a comma.