This is not how the Unraid cache feature works! The purpose of the cache facility on Unraid is to provide a faster perceived write speed when writing to User Shares than happens if you write directly to the parity protected array.
Under Unraid if you have a User Share set up to use a pool for caching purposes, then this is where and new file gets written (space permitting). It later gets moved across to the main array (as long as you have this specified as secondary storage) when mover runs (default is scheduled for overnight). The file only ever exists EITHER on cache OR on array - never on both.