The following passage is from Pride and Prejudice.
Mr. Bennet was so odd a mixture of quick parts, sarcastic humour, reserve, and caprice, that the experience of three and twenty years had been insufficient to make his wife understand his character.
With my limited knowledge of English, I know the following combinations are ok.
He was odd..
He was so odd..
He was a mixture of...
He was an odd mixture of...
But what does "so odd a mixture of" mean here? It feels like some words are missing in this phase. How should I interpret this phase?