REST API: Access Transaction flow

Hi,

I'm trying to retrieve information about Business Transaction flow using REST API.

On UI for a particular transaction, I can see the following:

I'm trying to retrieve the same data using REST API. I'm particularly interested in the persentages (68.1%, 2.2%, 29.8%). 

I do not see which method allows me to do that.

I've took a look at External Calls metrics for this BT, but that seems to provide different data. It only provides average response time, but if a business transaction makes 10 calls to BE, i'm interested in the SUM for these ten calls, not average between them.

Can you please tell me, which API should I use to achieve this?