get-posts-stateless - how to get 1st level comments?

[pangia]

There is a 'FetchSubComments' flag to set (which does not seem to work, maybe it is dependent on other flags?).

I see no top level comments option for this api call. I need to get all of 1st level comments for each post without having to call the 'get-single-post' api. is this possible?

[pangia]

Also cannot get sub comments to populate on get-single-post call.

Using:

get-single-post
{
"PostHashHex":"f31d16c810c6e3381fcc07553582bf2a07e4a655229e40dca9b7a5d18f398878",
"CommentOffset":0,
"CommentLimit":100,
"FetchParents":true,
"ReaderPublicKeyBase58Check":"BC1YLg7LJ54EfvEyCPqLFP3aUo9rPjNStwC4w73C3Me6yzzX2iiDry4"
}

The comment count of sub-posts is populated, but comments array is blank.