How to make looped animation take twice as long in parented layer?

Hi all,

In my composition I have two circles on separate layers, one large and one small.

The small circle has scale keyframes applied to it, which is then looped.

I want the large circle to mimic the scale animation of the small circle, which requires the following expression:

     thisComp.layer("SmallCircle").transform.scale

However, what I really want, is for the large circle to take twice as long to do the scale animation.

Say the small circle loop takes 2 seconds; then the large circle should do exactly the same, but in 4 seconds.

Of course when it's just two layers, I could just move the keyframes manually, but eventually I want to apply this effect to multiple layers and doing it manually would be a pain.

How can I achieve this by using expressions?

Many thanks in advance!