End feed antennas present a very unique challenge when it comes to comparing results and metrics. Despite a lot of erroneous information on the web, an end feed antenna requires a counterpoise of some type.
If you do not provide a very purposeful counterpoise of sufficient length, the antenna will use the shield of your coax as the counterpoise regardless of any unun, balun, or choke that has been installed.
Now consider how many different ways one can place the coax in an antenna installation. Some hang it in the air, some run it partially on the ground, some bury it, some run it next to gutters, some coil it up, some use long lengths of coax, some use short lengths of coax, etc. But in all of these cases, the coax is part of the radiating and receiving antenna. It should come as no surprise then when one installation cannot duplicate that of another!
And then even if you provide a purposeful counterpoise, how many of these are of unspecified length and run out onto the ground from varying heights? Again, no basis for comparison.
You should work on optimizing your installation. In general, more height is better. Experiment with a good choking balun on your coax and a purposeful counterpoise of various lengths in various orientations. With end feds, it is primarily a cut and try process.
And one final thought. If your coax is part of the radiating antenna, inserting an SWR bridge or antennalyzer will actually change the tuning of the antenna slightly. It can be a very frustrating cat and mouse game.