Nested Batches

Hello there,
I wanted to know if and how it is currently possible to use the BatchMapping with only one request for this situation:
Basically currently when mapping on type extension and field data it requested data from my server twice. Is it possible in this situation to avoid a second call and call everything in one go?

type Query{
  query: ReturnObject
}
type ReturnObject{
  id: ID
  header: [Header]
}
interface Header{
  id: ID
  description: String
}
interface Extension{
  id: ID
  data: String
}
type ObjectA implements Header & Extension{
  id: ID
  description: String
  data: String
}
type ObjectB implements Header {
  id: ID
  description: String
  objectC : [ObjectC ]
}
type ObjectC implements Extension{
  id: ID
  data: String
}

Start by reviewing the BatchMapping behavior described in the issue and the nested GraphQL schema example. Determine whether the type-extension and field mappings can be combined into one request, and document the supported behavior or the design needed to avoid the second server call.