Better yet, conduct double-blind controlled experiments. Oh but wait, no, it "cannot be forced" and the presence of a "skeptic" affects your results, I bet.
There's nothing unusual at all about maintaining as clean a "background" as possible in any scientific experiment. A microbiologist uses sterile agar plates, do they not?
For all we know, the conscious efforts of the subjects themselves could create too much "noise" for the "signal" to come through.
I have no knowledge of any double-blind, controlled experiment that was even
remotely relevant to anything I've experienced that could reasonably be attributed to "paranormal" phenomena. They're all about spoon-bending, levitating objects, zener card reading, and such circus sideshow bullsh1t.
An example of a
better sort of experiment would be to involve 2 subjects who think they have experienced such phenomena, but are living far away from each other and have not been in touch in years. Call them "A" and "B".
Have "A" take a journal of thoughts, with particular attention to who and what past experiences they are thinking about over a specified period, not telling them why. At some point involve "B" by discussing matters pertaining to A with B and/or bringing B into very close to the physical location of A (as one might expect an inverse-square relationship of such phenomena with distance), all without either party being informed of the nature of the experiment. See if thoughts about B begin to proliferate in A's journal when B is devoting more mental energy and/or is in closer physical proximity to A. See how the variance, if any, relates to B's mental activity pertaining to A vs. how it relates to proximity (preferably without B knowing they are near A, otherwise isolating the effect of proximity would not be possible). Time of day could also be a factor, as the nature of people's mental activity varies with time of day.
The sudden proliferation of such thoughts wouldn't necessarily
prove anything, but would certainly suggest that
some sort of thought transmission was going on between A and B, as would the absence of any thoughts of B on the part of A suggest that
no such transmission was going on. Not a perfect experiment, but a hell of a lot more relevant to the sort of phenomena I think
could be attributed to psychic activity than trying to read zener cards.