I wish you were upgrading your system to Catalina so you could format the external drive APFS and use Volumes instead of partitions, they are so much more flexible and you don't have to worry about how big to make them.
And you can add and delete them at will.
APFS was first introduced with High Sierra, to which Rita's contemplating upgrading, and as I recall, you reported during the beta period that you can switch from HFS+ to APFS seamlessly by just clicking on "Convert to APFS" in Disk Utility.
Under APFS, though, if you want to maintain an onboard clone it must be in a separate container/partition unless you run with SIP disabled (and even then, only CCC can do it).
The new Great Equalizer is the SEND button.
In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
