the distance between the floats and the fuse on the flyzone 60" beaver seems in proportion to yours so I dont think it sits too low from design, I think that weird water tail rudder is too much drag too far back and sucking the tail feathers too low not allowing enough ground speed to allow the tail to rotate
the WATER rudders on the flyzone beaver are on the back of the floats! so they dont suck down the tail feathers you could fab up a twin rudder system like the setup below or by inserting a servo in one of the floats and fab up required linkage...
my beaver will not break free of the water suction on the floats unless I use flaps too so maybe increase the travel on the flaps if possible to get full deflection??
you fly with a pistol too
....big cats around me
edit:
is it possible to raise that water rudder so that just part of the blade is in contact with the water to reduce the drag the flyzone rudders are the same size as that monster your dragging behind you and the flyzone is a 60" plane with 12" prop
it would be possible to cut your rudder shaft and make a few torque arms and replicate this setup .....
or just toss it in the air and have fun landing on the water.....maybe more work than you want to put into it