I have a question concerning adjective endings in nouns that aren't followed by "der" or "ein" words.
These adjectives receive the ending that would otherwise go to a non-present "der" word, like in the phrase: "Der Mann mit rotem Haar".
However, I come across a lot of sentences in German where a "der" or "ein" word is not present, but in English it would be, for example:

"Ich stimme Ihnen in gewissem Maße zu" - I agree with you to a certain extent.
"Ich spreche Deutsch auf sehr gutem Niveau" - I speak German at a very high level.

Obviously languages have different ways to express things, but I was wondering if someone could define when such a usage is made in German, i.e. in which forms of expression.

Thank you very much,