For something you expect Indexed shifting to work , the middle chainring will have the shifting easing features of pins and ramps
on the inside face..

where the inner most of a Double will Not ,it will be smooth , since it wont have a chain climbing up from another
smaller chainring to the left of It.

<shopping the Brick and Mortar stores ,that may also sell online & ship, you can call them on the Phone and Ask >