Literally, Shituf, שתף, means sharing, and one who shares ownership is called a Shotef, שותף , partner.
The rules defining Shituf-Hashem could be the same ones that define a business-Shotef.
Sanhedrin 63b, Tosfot's comment on the type Shituf that a Jew is allowed to let a non-Jew make, is a comment directly on the prohibition of forming a business-partnership (shotef) with a non-Jew. Here, the term "Shituf" is used interchangeably for the business-parntership (שותף) and the oath a non-Jew makes to a partner of Hashem (משותף):
"One must not form a Shotef [business partnership] [with a non-Jew]"
though they associate (shituf) God's name with "something else", we do
not find that it is forbidden to cause others to associate (shituf)"
So, if we want to know what amount of co-mingling is considered "Shituf" or "sharing" when we apply it to Hashem, then I think we can accurately define Shituf by looking how the Talmud identifies what percentage of sharing-ownership (Shotef) of a first-born-calf with a non-Jew is enough of a percentage to render the first-born-calf unnecessary to be redeem.
Bechoros 2b and Sanhedrin 63b use the same quote from "The Father of Samuel". So Bechoros 2b is definitely discussing the same exact business-partnership and oaths as Sanhedrin 63b
"The Father of Samuel" said: One must not form a partnership (שותף) with
a non-Jew lest he will be bound to take an oath to him and he will swear
in the name of his idol. ...
But the Sages say, so long as a gentile has a share in it (lit. has a
hand in the middle - any amount), it is exempt from the law of
Based on this, I think Shituf would include all of your examples and more.
It is any concept where Hashem shares any percent of his power with another entity/partner. Whether Hashem is 99.99% God and another entity shares .01%, or if Hashem has .01% and the other entity is 99.99% God, or anything between there (has a hand in the middle).
(ie. anything that violates "Hashem is one")
Avodah Zarah, on the other hand takes the next step of either making a physical representation to worship and emparting powers on something physical (eg. image, stone, wood, nature, bones), or saying Hashem isn't God at all, something else is (spiritually or physically). (ie. anything that violates "Hashem is God")
(or any of these practices of people who worship Avodah Zarah)
EDIT: Anything above on Sanhedrin 63b.