Here are some interesting archives of British 14" gun test on Tripitz armor. The tests however fall a little outside the results of the Facehard program. My only explanation is that they were done on small test plates striking 1.9 calibers from the edge so there could be some free edge effect.
Nathan Okun explained that the small plates were subject to shock effects and could not absorb the energy of the hit and broke apart. The comparison tests on British plate were apparently done on larger plates as two shots were put into a single plate.
Also Jeff Duquette made up a comparison of NaaB (FaceHard) to US Naval Ballistics tests.
US Navy tests on captured German armor plate.
From these documents