BTW, please pardon my ignorance if it shines now blindly bright:   wouldn't such orthogonalization of all EVs by default bias any subsequent contrast among EVs since it would allocate variance to preceeding EV for e.g. two equivalently potent ones thus possibly resulting in spurious contrasts?

IIRC in FSL orthogonalization of EVs is up for the user to specify -- what EVs should be orthogonolized to the space of what other EVs.