Strange but....

Why am I beating players 150 to 200 points higher than me over a series of games, yet losing regularly to certain players 150 to 200 points lower? 

You're probably trying harder against the higher rated players and taking the lower rated players a little for granted, I do that sometimes, I try not to but it happens anyway.

It's due to type advantages, like in Pokémon. A fire-type pokémon, for example, can beat a grass-type that's many levels higher, but it can also lose to a water-type that's many levels lower.

I wondered the same thing aloud upon seeing a Nicki Minaj photo.

You need the Silph scope to preperly identify Nicki Minaj.

Sample size is not large enough. Over 100 or so games, you will find more losses to the higher rated players.