Just to clarify or confuse, once the mains are set to small you won't be able to use the plus setting anyway, even if it allows it to be selected, my Denon does this, the programming won't allow it to work that way, the small setting overrides the plus sub setting.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70