When sacrificing for shards, the box that shows you how many you'll be getting claims that there are rarity and premium bonuses. The bonuses that say "x2 recovered shards" for both rarity and premium don't seem to be applying. As example here is what my snowman says he gives:

Spoiler

Shards reward details:
Level and tokens: +117
Embedded shards: +0
Age: +1084(~542 weeks)
Transfers: rarely transfered, no penalty
Rare: x2 recovered shards, x2 age bonus
Premium: x2 recovered shards

The altar says this snowman gives a total of 1201 shards when sacrificed, when it looks to me like it should be 4804.

I think the recovered shards might only be about the shards that are already embedded. 

Ah you're probably right.

I am going to say that this is intended (currently) as Mur has given little information to people publicly about the shards.