There is a problem while using the sparky-installer on a drive that uses the Global Partition Table (GPT) used by EFI. The installer script uses fdisk which doesn't support GPT and displays it always as a single partition. This in turn causes the installer to remain blind to the partitions created within GPT.
This issue will be fixed with the new installer. I'm linking the installer ticket here: https://sourceforge.net/p/sparkylinux/tickets/8/