What is the secret to Ranked Placements?

I've played placements on 4 accounts.

None of these accounts have played Ranked before.

Account 1: Wins game 1. Placed Bronze III.

Account 2: Wins game 1. Placed Iron II.

Account 3: Loses game 1. Placed Iron II.

Account 4: Loses game 1. Placed Bronze II.

On average they all gain 46-63LP per win afterwards. All playing with/against Silver III - Golv IV.

What is the highest rank you can achieve after game 1 of placements?

What are the conditions you need to achieve this?

Are Ranked Placements on new accounts just RNG?