ventilation duct section using dynamic block

[Macieto]

Hi,
Im trying to create ventilation duct section using dynamic block. Duct section consist on:
1) outside circle (dashed) - it stands for insulation fd the duct.
2) concentric inside circle
3) "moon" inside.

In this DB I would like to be able to manipulate:
1) diameter of the outside circle (dashed)
2) diameter of inside circle
and I would like the "moon" to be scaled while Im changing diameter of inside circle
I was trying to do thatusing constraints and using scale parameter. Both blocks you can see in attached drawing. As you can see I cannot achieve my goal. My DWG file in the attachment.

Any help will be apriciated.
duct.jpg

[clshade]

You have requested Concentric inside circle and to be able to change it on its own.
Do you wish to do both?

[Macieto]

Yes.
I have almost achieved my goal using DB with constraints parameters (block on the left in previously attached DWG), but what I cannot achive is changing the scale of the "moon" inside while I change diameter of inside circle. So when I change parameter "DN" to "1000" than "moon" remains the same, but I want it to change scale while changing "DN". General "DN" parameter and "RAM" parameter works fine. "Moon" is the problem that remains. See attached picture below.
duuct.png