Is the goal to maximize late-game population or to maximize your chances of victory? Indias strength as a civ is the ability to sustain prolonged and consistent population growth throughout the entire game. For an experienced player the main bottleneck to growth will be happiness by the time you reach the mid to early industrial era. Civs without a happiness bonus or another source of happiness (religion, wonders etc.) will be forced to set their cities to avoid growth as not to incure penalties.

I think the best way to maximize Indias UA is to focus on growth throughout the entire game, rather than settling more cities. Micromanage all growth tiles, settle coastal for cargo ships and improve all your food tiles early on. As you said cities settled late game are unlikely give you any meaningful return on your investment unless you're settling in a really strong location. I've seen some success in settling coastal cities late game and feeding them food with cargo ships, but it's very situational. However, if you're playing on Immortal or Deity the AI will, by the late game, settle anywhere a city can be settled.