I use Acronis. The basic way it works is that it does a full then incrementals thereafter. It will only keep a certain number of incrementals at which point it merges the oldest incremental in to the full thus creating a new full. The sync program would have do to it by "block" or whatever you want to call it or it will continually be trying to sync the huge full backup every day.
The perfect way to do it would be to back up nightly to a NAS or big External Hard Drive and then sync that hard drive or NAS to the cloud. Same issue with merging the oldest incremental in to the last full thus creating a new full. So does anyone know of a sync program that is "block" aware of wherever you want to call it?