I'm going to answer your point from the FE perspective.
If the experiments are indeed genuine (the distinction of 'amateur' carries no weight, since the deep state/shadow govt has legions of undercover personnel doing all kinds of things as relatively convincing 'amateurs,' including doing phony/junk/disinfo research on conspiracy-related matters, surely as well as posting all day in this and other forums; it's a shame that they have cast doubt on and complicated well-meaning, real amateur research activity, but that's where we are) the findings could be due to a misunderstanding of the media at certain altitudes. The various FE models often posit a crystalline, glass, or metal dome and layering of heavens, and also maintain the existence of aether, which is still asserted to exist by some academics and was only said to be disproven by two non-public experiments. Taking dome-multiple heavens-aether as true, the various mediums encountered - perhaps denser than near-Earth air/aether - may be slowing the waves and making the distance seem greater than it is. As far as I can tell they're not able to do the bounceback with other planets, so they can't compare the Venus findings with that of others. The vast majority of radio waves don't penetrate the ionosphere, and I haven't seen evidence of credible tests, if there can be any, that involve super-HF test signals going out and not coming back. I don't believe man has ever gone above the neighborhood of 40-50 miles altitude (which is the approximate altitude of the provably faked Apollo video of Earth; and where the 'ISS' appears to be unmanned satellite), so there's been no direct verification of what's above (only a tiny lower portion of 'first heaven' in the various models), and the credibility of the agencies/people who might go there (or claim to have conducted highly advanced radio testing) in the future is at/near zero. If super HF waves are able to partially or fully penetrate the firmament, resulting in no or misdirected bounceback, it would be difficult to prove RE using radio alone, based on the technology and experiment methodology used thus far.
As applies to radio experiments, audio fakery also cannot be discounted. Satellites may be able to automatically receive morse-coded Venus-targeted super HF radio transmissions and/or be aware of their broadcast beforehand and send them back at a heliocentrically appropriate timing. This wouldn't have to be done in many instances, just for a handful of government and amateur tests to be cemented as undeniable fact, at which point people, accepting the fakery, would probably decline to go through the expensive and apparently pointless exercise of trying to repeat the results. If the satellite operators missed any tests, the planet could be thought to have been missed, or something else went wrong; in any case the failed experiments wouldn't likely be reported by the media or be of interest to more than a tiny percentage of the population.
With regards to orbit observations, another potential explanation that hasn't been mentioned is Tychonic/Egyptian 'geoheliocentrism' (essentially a form of geocentrism). In it Mercury and Venus orbit the Sun (explaining transit), the Sun orbits the Earth, and the other planets orbit the Earth at an altitude higher than and orbit broader than the Sun-Mercury-Venus system. It seems possible that an elliptical-orbit form of the Tychonic model (known as Modified Tychonic / MT) is consistent with most observations, if relativity, which is fraught with indications of establishment promotion and fraud in the form of Einstein, is found to be a false concept.