For ground effect to be a cause the lower wing has to be les then 1/2 chord width above the ground, and providing enough lift to fly the model. I doubt `Ground Effect' is in any way implicated here. It sounds more a combination of normal taildragger stuff, wheels too far foward of the CG, rudder effectivness low at low speeds, possibly blanked by the fuselage at high aoa's and torque effects as the tail rises. Try these `fixes' one at a time. See if you can move the wheels back a bit, with some ally u/c's you can turn the whole thing around. At flying attitude the wheel axle should be about 15 deg. foward of the cg, i.e. on a line drawn at 15 deg. through the cg. As the takeoff is commenced try using foward elevator stick to raise the tail as soon as possible, this will help the rudder bite in the prop slipstream and provide positive yaw control on the ground. Try not using full power, 75% should be enough to take off, and there will be less torque effect to have to control. Try not using ailerons until the model is ready to turn on the crosswind leg after takeoff, biplanes are RUDDER airplanes, not aileron airplanes, make sure you have at least 45deg. rudder movement each way. Then go out and practise lots of touch and goes, using RUDDER lots, and only rudder when the wheels are on the ground. Good luck!
Evan.