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I am not sure if and in which cases I have to use a comma before "that". Consider the following examples:
The first point is, that [...]
One major problem about financial returns is, that they are [...]
In [...] one can see, that both tails are heavier.
The model implies, that the returns insist of a [...]
I am not sure about the commas in this context.
None of the examples you gave require a comma. As a rule of thumb, you don't use a comma before a clause that begins with that.
You're veering to the territory of restrictive and nonrestrictive clauses. A restrictive clause limits the meaning of a sentence when you remove it. A nonrestrictive clause doesn't. Here are two examples (forgive the passive voice):
Restrictive: The rules of grammar that are obsolete should be ignored. Just the crusty old ones that I don't agree with.
Nonrestrictive: The rules of grammar, which are obsolete, should be ignored. Yes, all of them!
As you can see, they are very different sentences.
Personally, I would remove all of them.
In general, that is not introduced by a comma, as this would separate the two sentences which that (conjunction) links.
Besides, when you use that as a relative pronoun, you cannot use it in non defining sentences (where you use which), but these are the only ones where a comma is needed, to separate them from the main clause.
Summing up, all the sentences you have provided can do without commas before "that".
