In v10 for 1.12.2, I've found myself 10-20,000 blocks up, and traveled 3-10,000 blocks forward using the magnetic forcefield.

The easiest way to replicate this is to get in player-high water, place a block over yourself, activate the forcefield, and move out from under the block. Another way is to get in a boat before activating the forcefield, then exit the vehicle. In both cases, the ground will probably go away in a hurry.