Is there any way to set the percentage value of each headline?

By default (33%, 33%, 33%)

* L1 Heading [33%]

** DONE L2 Heading

** TODO L2 Heading

** TODO L2 Heading

I would like (20%, 50%, 30%)

* L1 Heading [20%]

** DONE L2 Heading

** TODO L2 Heading

** TODO L2 Heading

Thanks.