When you move to the ground your dog won't know what force fetch means in the different situation. Start at square one again as if you are starting ff all over again. He'll pick it up this 2nd time quicker than he did the first time but there will be a learning time for him to "get it" once he's on the ground. When he's got it on the ground you can go ahead to walking fetch, stick fetch, baseball, pile work, and to the rest of basics.
My plan is to work on hold and ff on the table then move to the ground for walking fetch and stick fetch. Is that a practical plan or should I deviate from it somehow?