How is the あ vowel produced? I've been reading about the sounds of Japanese and always thought the 's highest point is shown as in this diagram:  But reading more, I stumble upon for example from the Japanese wikipedia this one: ![enter image description here]( Which one would be the most correct in most cases?

Both are correct, there is no set-in-stone answer as the difference in pronunciation is slight. As you said, the pronunciation depends on context.