Normally, VP saves to the folder used by the source files. Thereafter, using SAVE overwrites the VPJ file in that folder.
Use Save AS once, to another folder, and that folder becomes the VPJ Save AS location, and remains so even if another project is later opened via the caret to the right of the Open icon | recent files drop-down menu.
If instead a VPJ is opened via Menu | FILE | OPEN PROJECT FILE, then the Save AS choice will switch to the folder where that project resides.