Hi Josh, it's not so much that the angles may not be the same without the riser.
It's more to do with the length of the stroke with the stone using the the new arms and "no" riser.
You can see in the pics that the top part of the stone can't be used.

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It seems the riser was included to allow the ball joint addition.
See point "A" is roughly the same.

The new crossbar was added for a couple of reasons.
The first being a "belly" was found on the old crossbars and the tighter fitting new "L" bracket wouldn't fit.

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The second was the ability to achieve more acute angles (13°) and therefore an angle dimple location revision.
While this thought was going around, a longer crossbar would also offer 35°.

I would like to try an even thicker riser and longer arms.
So the full length of the stone can be used.

Very smart observations, Chris! I never looked at it this way. I guess you're an engineer as well?