My understanding from the Perpignan report is that, with autotrim in operation, the THS only moves when the elevator goes past the neutral position: nose down elevator will command the THS to move more nose down. The elevator follows the (g-driven) SS orders. So a small nose-down command from the SS that causes the elevator to move from nose-up to less nose-up without going to nose-down will not cause the THS to move.