The following would appear to address most if not all of the various issues and objections:
There are 27 trials.
There are 3 opaquely lined envelopes per trial.
There is 1 photograph with an image and 2 blank photographs in each trial's set of envelopes.
Pavel chooses one envelope per trial after examining all three as he desires (if necessary, within a pre-set time limit).
A successful trial (hit) is choosing the photograph with an image.
The result of each trial is revealed immediately after each trial.
The image(s) can be the same for all the trials, or different for each trial, whatever Pavel thinks would be most helpful. He may be shown a copy of the trial's image or told in words what the image depicts at the start of each trial if that would be helpful.
18 hits in the 27 trials (2/3 or better correct) is a successful test. The probability of success by chance is well under 1 in 1000 (.000407). The probability of 17 hits or better by chance is .00154.
The success rate needed for success corresponds to getting 27 or more hits out of 40, something that appears to be more comfortably within Pavel's claimed success rate than 30 out of 40.
Note that the total number of envelopes involved is only one more than in the 40-trials protocol currently under consideration.
(If I'm interpreting Pavel's comments correctly, he suggests failures occur when he is unable to perceive the future opening of an envelope showing a target picture when the envelope does in fact contain the target picture -- in other words, false negatives. If that's the case, then the presence of the two blanks instead of one in each trial set should not decrease the probability of success per trial, given that the examination time he would have available per envelope would be the same.)
Respectfully,
Myriad