I was asked about it, so I went and tested and Tranquil Heart is a separate term from gear Enmity, and Enmity from Atma is still hit by the gear cap as we would have predicted.
Character 1 (0 Enmity): Sleep Pull (201 CE), 3x En-II spell (240 CE), 1x Cure for 0HP (1 CE) = 442 CE
Character 2 (-24 Enmity in gear, Minikin, Crimson Scale = -54 total, capped to -50): [2x Cure V (800*N CE), 7x Carol (140 CE)]/2, 8x Cure for 0HP (8CE)
((442-8 )*2-140)/800 = .91, so Tranquil Heart is still -9%
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