Sham meditation procedures necessarily involve deception of participants and the ethicality of this in clinical trials is open to dispute. Further, this kind of strategy can be logistically challenging and there is always a risk that the deception might be uncovered, thereby immediately invalidating the entire study.
The fact that some techniques elicit detectable effects when compared to sham procedures while others do not implies that some meditation techniques may not have specific effects whereas others may well have such effects. This logically suggests the possibility that the genre is not homogenous and that the use of meditation versus sham studies offers a method by which specifically effective techniques may be separated from those that are not.
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There may be one remedy for that. Tell the participants afterward that they were given a sham meditation technique. If it’s a year long study, then it’s still a problem during that first year. It’s definitely a dilemma. I know I wouldn’t want to practice a technique knowing it’s a sham.
Some controlled studies have a group of people meditating regularly and a control group of those who do not. That can be sufficient for science. The sham groups are probably just used to determine a placebo effect. Very tricky.