Hi guys,
I wouldn´t waste my time with the K4 ciphertext.
IMHO, the K4 ciphertext is mumbo jumbo, a red herring.
Mr. Sanborn described it as ‘THE PASSAGE DEBRIS, THAT ENCUMBERS THE LOWER PART OF THE DOORWAY’ and that HAS TO BE REMOVED!
I think this is very clear, isn´t it?
So if we remove the K4 copperwall ciphertext, we need a NEW CIPHERTEXT. This is what Ed Scheidt called the ‘masking technique’. If you have a ciphertext that could never be transformed into a plaintext, I would say this is a perfect ‘masking technique’, isn´t it?
But where to get a new ciphertext? Well, that´s easy, it´s explained in K2:
THEY USED THE EARTHS MAGNETIC FIELD. THE INFORMATION (K4) WAS GATHERED AND TRANSMITTED UNDERGROUND TO AN UNKNOWN LOCATION.
What is the slogan of the KRYPTOS artwork?
INTELLIGENCE GATHERING / INFORMATION GATHERING.
So the slogan is a clue to the THE INFORMATION, described in K2.
The EARTHS MAGNETIC FIELD is a reference to the compass rose outside the CIA building and THE INFORMATION is of course the morse code message itself, known as K4, which was transmitted to 37 … 5 … 77 … 45.
The morse code message has exactly 97 letters. 81 letters are visible and 16 letters are invisible under the stone slabs ‘BETWEEN SUBTLE SHADING AND THE ABSENCE OF LIGHT’, which characterizes the space between ‘VIRTUALLY INVISIBLE’ and ‘SHADOW FORCES’. So K1 delivers the missing invisible 16 letters in the form of the anagram ‘NUANCE OF IQLUSION’.
VISIBLE MORSE CODE + NUANCE OF IQLUSION = (NEW) K4 CIPHERTEXT.
But that´s just my opinion 
Greetings from Europe
Frankyboy