Don't get the gear too far out in front or you will be enjoying some impressive spin-outs & ground loops. I keep my axles directly under the leading edge. In addition to having the gear too far aft, nosing over can be caused by several other things: landing gear too flexy-- thus deflecting backward over bumps, too much toe-in -- thus producing a lot of wheel drag, too much toe out -- same drag problem plus really squirrely take-offs & landings, wheels too tight, wheels too small, grass too thick/deep.