My Explorer was tail-heavy too. I initially shoved the tailboom further in, but it wasn't really enough to eliminate ballast entirely, plus it didn't fly as efficiently that way. Extending the nose was the way to go. I lengthened mine by 3" before the bottle neck. I did that because it gave me more room to put things in the nose, such as a camera; the bottleneck area is barely tall enough to hold the battery alone. I love the method you used to graft an extension to the battery platform, very elegant and pleasing, and a simple trace. I didn't think of that, and just did a square cut.