How to set chunk sizes in Azure OpenAI vector store

Question

We're switching from OpenAI to Azure OpenAI which works fine so far. We're using Assitants with "File search".

Unfortunately the settings for chunk sizes (and overlaps) are being ignored creating vector stores. A different size of chunks, other than the default 800 and 400 for overlaps, is absolutely crucial to our process.

Is this feature not (yet) available? Must parameters be set differently, than this?:

chunking_strategy: { type: "static", static: { max_chunk_size_tokens: 2100, chunk_overlap_tokens: 1050 } }

Might there be an alternative for use with Assistants, if this feature is not available?