which is higher the greater ...

Hello,

I have little confusion over the following sentence

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Therefore, a maturity risk premium (MRP), which is higher the greater the years to maturity, must be included in the required interest rate.
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Does it mean that "the higher MRP is, the greater the years to maturity is"??
If not, how should I paraphrase it?

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The velocity approaches a limiting value, which is higher, the greater the diameter of the tube.
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This is a sentence I found on Google Books.
Does it mean that "the higher the limiting value is, the greater the diameter of the tube is"?
But there is a comma after "higher"...is the comma redundant?




Best Regards

The longer to maturity, the higher the premium.

We often put commas in these phrases, but I wouldn't use one in that example because it separates the second part from the verb.