You are right to raise this. I suggested the same thing when pies first came out, and it has been discussed previously in the community and I think staff are aware that this is a feature which some people would like. Adding to positions in proportion to existing holdings, ie by shares, would allow one to mimic the way an ETF is run. The staff have already mentioned that one of the developments that may be in the pipeline is pie-ETFs, with weights of the contained investments automatically provided.
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