buoyancy problems

Anyone know why custom body water in water test map works perfect with buoyancy example cube, yet in my project, only works if the depth of custom water is low enough, unlike test map that no matter how much I scale on z, it always floats cube on top perfectly, not so in my project, as i increase z on cube, cube BP from engine water area as noted above, falls through and always, stops , in the middle,. Odd ?