Distribution on a list

Greetings. I am trying to design a louver, which consist of different dimensions of sticks. They are random arranged, either the space between them. My question is, how can i make a distribution on those space to make the louver look dense at some part.

Here' my method toward those space creating.

First, i create a numeric combination, so i got 3,9,15,30.

Second, i repeated the data until the length i want, and jitter them. Here's what i get:

30,3,9,3,15,9,30,30,15,3,3,15,30,9,3,3,15,3,3,9,9,3,15

Actually what i`m trying to achieve shown below:

3,9,3,3,30,3,15,9,15,30,30,15,30,3,9,15,9,3,3,15,3,9,3

My idea is, to make the center part look no so dense compare to others part, somehow

it's no a absolute looking in the final. What i mean is, maybe more [30] like 80% drop at the center part, 80% of [3] drop at the start and the end, meanwhile the others 20% [3] and [30] appear to be random in whole series. 

Last, i will weave this set with other set which stand of the dimensions of sticks.