This is what you need to do. In drafting first go to the Annotation toolbar and click on Offset center point symbol. Here you can play with the positon of the center point of the arc. In the offset center point symbol window in the offset option select Vertical Distance from from arc. Choose a distance and select the arc you want to dimension and click OK / Apply. This will create a new center point. You can see this by the + mark on your screen. Now go to dimension toolbar and select Folded Radius Dimension. Select the arc you want to dimension and select the new center point (+) now click in a space between the arc and the new center point.
In drafting go to the Annotation toolbar and select Offset Center Point Symbol. With this tool it is possible to manipulate the center point.
In the Offset Center Point Symbol window in the Offset option you can choose in which direction you want to manipulate the center of the arc. For this tutorial I choose the Vertical Distance from arc. In the Distance box type in the distance that you want.
Select the arc you want to dimension. For this one I'm doing the same as you by selecting the arc on the inside. When you select the arc you will see a + on your screen. This is the new center point. Click OK / Apply and close the window.
Now go to the Dimension toolbar and select Folded Radius Dimension
Select the arc you want to dimension and select the new center point created earlier. Now click in a space between the new center point and the selected arc. And there you have it a Folded Radius
This pic is just to show the Folded and Un-Folded Radius next to each other