Provisional system rewards you with a punch in the mouth...

So mid-season I hit level 30 and start provos for solo-queue. I know the game, but I didn't "know the game" at the time, but managed somehow to place Silver 4. I didn't like ranked play as much as normals and decayed to 5, and then tried to promo back up, ended up falling into Bronze. Went on tilt playing only ranked until I hit B5. Flash forward to the problem.

I'm a better player now, I fill positions, I understand when to team fight, I have a wider range of characters I play and can counter against. I started a ranked team to go after ward rewards and to see if I had improved. My team went 3-2, all of our wins were 20+ min surrenders, and one loss was close, the other a blow out.

We placed Bronze 4.

I don't get it. I managed to build a team filled with people in Gold and play at that level successfully. Play at an MMR more than double what I do in solo-queue, and I'm rewarded with Bronze 4? I wasn't expecting to be put very high, S3, maybe even push S1 or G5 if we had won all 5 games. But I just can't reason with a B4 placement.

Someone feed me some knowledge on how this works, I'm missing it.