Actually, it would go more like this:
Q: Officer, how did you determine that my client had a pistol in his waistband?
A: I saw indications of "printing" and got glimpses of what might have been a pistol, so I investigated further. As I did, I realized that he did, in fact, have a pistol which was mostly concealed by his clothing. The only part which was visible was a portion of the top of the pistol.
Q: You say that the pistol was partially visible, so that anyone would have been able to tell that it was there?
A: No, sir, I said that the pistol was mostly concealed. As a law enforcement officer, I have been specifically trained to notice details and to recognize when a person is concealing a weapon, even when it is not plain to other people.
Wearing the IWB as if it were a standard holster -- outside the clothing -- eliminates the whole issue.
And, of course, you are 100% correct about some positive form of retention being important.