Rules for rising and falling intonation in similar questions - what are they?

Consider these two questions:

Would you mind saying a little bit more about that?

and

What do you mean by that?

When they perform the same function, and I expect an answer to both, why does the first have a falling intonation and the second one which rises?

My group of learners are as puzzled as I am - what suggestions does this group have?

Formally, they are not the same. The first question is a yes/no question (“Would you mind?” “No, I wouldn’t.”) and the second question is an information question (“What do you mean?” “I mean what I say.”) In standard English, a yes/no question ends with a rising intonation and an informational question with a falling intonation, but there is considerable variation between and dialects.

Personally, when I say “What do you mean by that?”, I would end the word “that” with a rising intonation, to show I am asking for information but, for added emphasis, I might start the word “that” with the opposite intonation. So my voice would go up, and then down.

Similarly, in “Would you mind saying a little more about that?” I would end “that” with a rising intonation, because it is a yes/no question but, to add emphasis, I might start it with the opposite intonation. So my voice would go down, and then up.