Opera La bohème's outsiders shown proportionately (2,5)
I believe the answer is:
to scale
'proportionately' is the definition.
(I've seen this in another clue)
'opera la boheme's outsiders' is the wordplay.
'opera' becomes 'tosca' (Giacomo Puccini opera).
'la boheme' becomes 'loveandadime' (I've seen this in another clue).
'outsiders' means to remove the middle letters (only the letters on the outside of the word remain).
'loveandadime' with its centre taken out is 'le'.
'tosca'+'le'='TO SCALE'
'shown' is the link.
(Other definitions for to scale that I've seen before include "Accurately represented" , "how a model may be made" , "In proportion" , "Matching original" , "properly modelled" .)