Think it's only for the NLDS. Once they go to the NLCS, top seed gets games 1, 2, 6 and 7.
Maybe I am wrong, but if Nats are top seed, and sweep the NLDS and win NLCS in 5, it could be:
NLDSAway - W
Away - W
Home - W
NLCSHome - W
Home - W
Away - L
Away - W
Away - W
That's 3 home games.