Check the derivation path related functions at the end of the file: https://github.com/spesmilo/electrum/blob/master/electrum/bip32.py#L276-L343
EDIT: Actually, it's probably more clear in the base_wizard.py: https://github.com/spesmilo/electrum/blob/fb76fcc886b7c999387a6676f479678df742fdaa/electrum/base_wizard.py#L397-L399
You can see if sets up the derivation points there based on user choice of type... this then uses the bip44_derivation() function in keystore.py to set the path: https://github.com/spesmilo/electrum/blob/fb76fcc886b7c999387a6676f479678df742fdaa/electrum/keystore.py#L791-L793