Are you putting a bobbing platform on it? If that's the case, it's gonna have to be a thick platform, and the geyser will have to move fairly slowly. The other option is to have the bobbing platform just be a regular FOF moving synchronously with the geyser.
Did my example WAD work the way you wanted it to, though? If so, there's not much more I can say:
Make sure Linedef Type 4 and 2 are exactly the same length.
Make sure the floating block has the same sector height (difference between ceiling and floor) in the FOF control sector itself as well as both the control sectors that determine its min and max heights.