Link zu #1 https://www.collinsdictionary.com/dictionary/... (steht dort gleich oben zu BE)

Ich habe es jetzt nachgelesen, aber ich gestehe, dass ich nicht wusste, was "postpositive" bedeutet. Ich fühle mich auch jetzt nicht firm genug, um eine Definition zu präsentieren.

“postpositive” : positioned / placed after the item modified:

A well-prepared guide was waiting for them at the hotel.

The guide waiting for them at the hotel was well prepared.

Normally, "postpositive" refers to things placed immediately after a noun, as in "He acted like a man eaten up by rage".

Looks a bit funny here, as what they mean is just that it isn't in front of a noun.

A well-prepared man = a man who was well prepared.

Verstehe ich das richtig, dass es im Satz im OP "well prepared" heißen muss, weil es auch da postpositive ist? Das hatte ich ohnehin vermutet, aber nach #1 war ich nicht mehr sicher.

According to that rule, yes.

It's not universally applied, however. Many other dictionaries (e.g. Oxford) don't seem to care.

I would naturally write it without the hyphen, that is, instinctively following the postpositive rule (now that I have a name for it!)

As CM2DD points out "postpositive" strictly means occurring immediately after the noun (or pronoun).

"predicative" describes the case where the adjective follows a verb, "attributive" where it precedes the noun:

a well-prepared hiker (attributive)

a hiker I thought well prepared (predicative)

anyone well prepared (postpositive)

Good example, Bion! Couldn't think of a decent one.