“G28” is the command to go to a specific position, relative to the machine home that is established by the limit switches. “G28.1” is the command you issue from the console that tells the machine to “store current position as G28 home.” That position is retained after power off, so if you power back up, home the machine, then issue “G28”, it will return to that exact position. Remember, this is relative to the homed position, so you will need to MAKE SURE you home the machine when you start up! If you don’t, results can be unpredictable.
Since G28.1 orders the machine to set an exact position, it will return there in X, Y, and Z each time. This is independent of your tool offset set with the touch plate. So you are correct about what you have to set.
I would suggest homing your machine, jogging until your tool is exactly at the 0,0 point of your fixture, then homing the Z, which will put it right up at the top of its motion range. Then zero it out, and issue G28.1. After that, each time you call G28, it will return to that exact position, at your fixture’s 0,0 with the Z up at the top of the range. That’s where it will go to at the beginning of every Fusion job, and it will end there as well. Which makes it really convenient for changing tools. Once it’s there and you hit the zero button to set your work coordinates to 0 relative to that spot, you can jog freely and run your z-probing cycle just like normal. It basically just gives a safe position for the tool to go to at the beginning and end of each run, as well as automatically zeroing your X and Y to your fixture between power-downs.
EDIT: For a really good write-up on it, check out this thread here: Learning About G28