Kirk the ENG OUT CRZ page is for 'info only' - Not executable so the new active N1 idea is not possible.
Though you are correct that when the EO CRZ page is selected 'the FMC accounts for wing and engine anti-ice, air conditioning, and the engine bleed of the operating engine'
Just to highlight the original posters question - he was questioning why the difference between
LT ENG OUT MAX ALT - say FL187
and
RH ENG OUT MAX ALT - say FL190
The couple of hundred feet is not the major issue but the L/R reasoning is.
Hope I didn't misunderstand your post.
Thanks