German vowel charts used in the wikipedia article Standard German phonology do not locate vowels with great details. For example German [e] is a bit higher than the IPA [e] or tense vowel [e:] is not produced exactly in the same location of its allophone short vowel [e]. the wikipedia charts are phonemic oriented for example [e:] and [e] are grouped together as "e(:)"
In Feb 2017 I asked (in German): "How many vowels are there in German language". Maybe it can help you a little bit: Wie viele Vokale gibt es im Deutschen?
In this question I listed 30 different German vowels, because I counted stressed and unstressed vowels as different vowels, also long and short.
I think you can't get it more detailed, because there are almost 100 million native speakers from more than a dozen nations all over the world (most of them in Europe, but some also in Australia, Namibia, South Africa, USA and Brazil).
We all pronounce German absolutely correct per definition, since we are native speakers. We (as a big group of many million people) define what is correct. There is no other authority than us native speakers who can define this.
But we are a very heterogen group. Go to Dresden, Berlin, Hamburg, Cologne, Bern, Munich, Vienna and Merano and listen to the people there. Also listen to the local radio stations. When you walk though these 8 cities you will hear significant differences in the pronunciation.
An Example: The [a] sound in the article »das« is significant different when produced by a typical speaker form Munich compared to a speaker from Vienna or from Dresden. (Munich, Vienna and Dresden lay at the corners of a equilateral triangle with a side length of about 360 km)
But there is no need to travel through different cities. In some cities you can hear differences even between young and old speakers, or between rich and poor people.
Standard pronunciation, practiced by professional speakers, is most often not the way how the majority of people speak at home with their family members, or with their friends in a bar. And even the way how professional speakers pronounce vowels is different, when you compare speakers from Switzerland, Austria and Germany.