OCFMasters spent two years delving into the ins and outs of End Fed antennas. Throughout that time, we discovered that most End Fed antenna transformers used higher impedance transformations than necessary and were wound in a way that limited the high frequency response of the transformer.
We also found that applying the capacitive loading technique we applied to OCFs worked very well on End Fed Antennas with low SWR on all bands. An often-overlooked item was the need for a properly sized counterpoise, either wire or coax. See the diagrams below. For convenience and simplicity of installation, we recommend a coax counterpoise.