Dodging a queue does not affect your MMR but your LP so it doesn't count as a loss. If you dodge a game in your placement games you will not be affected that much, however if you dodge lets say 30 games in these games, you will still end up lower than expected, since the LP are already getting calculated by the system.
You were S5 in season 3 and now you Play your 5 games. 3 wins - 2 loss. You will most likely be placed in silver 4.
If you dodge 5 games and play 10 you will be placed in silver 5 but with an mmr of silver 4.
Now this is only an estimated placement. I don't know how the exact formula works.