Hello Richard
Nice results, I tried lost foam casting some time ago, the results were generally easier ( I found ) with foam over sand, you made a analogue of the finished part in foam, I used blue insulation foam, made a riser of foam then dipped the part in wet water ( a wetting agent ( soap added )) then dipped it in a runny plaster mix - any air dry one will do, let that dry, placed it into a container ( metal

) and filled the container with sand.
When the ally is poured in, it melts the foam, using the plaster meant that ALL the detail on the foam was replaced by ally.
Best regards with your endeavors.
Ed