Yeah, the top and bottom wicks can be different in spot and futures and also the value may differ little bit in different exchanges.
However i do have heard complains that exchanges manipulate the future market for their favor.
There are just some differences and we cannot really verify those accusations. I think the ones who has capability of manipulating are the whales since they have deep pockets and influence the volume that they have.
This is from the link posted by TryNinja. I will just quote it for those who haven't checked it out and read it as well, OP.
4. Futures vs. Spot prices - Cryptocurrency prices are determined by buyers and sellers through an economic process of supply and demand. The spot price is the ruling price for all transactions in the spot market. The futures price, on the other hand, is based on the prevailing spot price plus the futures premium. The futures premium could be either positive or negative. A positive premium indicates that the futures price is higher than the spot price; conversely, a negative premium indicates that the futures price is lower than the spot price. Changes in supply and demand may cause the future premium to fluctuate.
This is the best explanation that you could have with this.