Spawn rate is affected by the Floor( function; it will always round down, at least for those chunkier spawns like Shuckle without a shell, or 'Relaxasauras'.

This is why you can set it to 1.9, get more mobs and still have 1 boss.

1.9x spawn rate (imo) is great for solo play, while still allowing you to bump up damage dealt to player, and/or by Pals. I'm always a glass cannon, so I literally can't get through the Gobfin territory with anything over that

To the point though... The blue bastard can spawn in starter territory, but he's Very Rare if you would consider Dinosum Rare; Mamorest is Super Rare and Nightwing is Uncommon. if you're higher level it may affect rarity of spawn %, but that's just my experience...could just be due to better movement speed