the mBSC seems to act as a “repeater”, so I would say you need to connect the antenna feeders from the BTS (top of cabinet) to the mBSC (inputs).
Which brand is it ? Looking at the product description, you should see which input connectors are available.
I think the length of feeders from BTS to mBSC can be rather long (around 50m probably) as long as you are using feeders bigger than 1/2″ (7/8″ for example). That’s just an assumption though.