Hi, @Thebroughfamily,
The only situation where sysupgrade seems to fail is when you extended your root partition, otherwise, it just works as expected and does not wipe you configuration.
I explained in this post how to keep configuration between upgrades if you use Image Builder, even when you have to do a full install wiping your card: Raspberry Pi 4 released
And, the problem with Image Builder and setting the root image size it's that you will need that free space in your drive, just in case you are using a VM take it in account, as I ran out of space in my Linux VM because of this.
Hope this clarifies, mate.