I'd bet that you can get close...  You can set the tiering policy for the LUN individually, but there isn't a policy that equates to "middle tier".  There is, however, a policy for "no data movement", so what I'm thinking is that you may be able to get the LUN to a state where none, or at least a minimal amount, of it is in your tier0, and then just tell it to stop moving.  I might try changing some other LUN(s) in the pool to 'Highest Available Tier' for a few days to see is they can force it out of the SSDs, then change the one you want to no movement, and then set the others back.  Less obtrusively, you could change this particular LUN to "automatic" and watch to see if that reduced or eliminated his tier0 allocation, and then change it to no movement if you get it to the state that you are looking for.  It would be easier if you wanted it to live in the lowest available tier, as there is a specific policy for that.  I'll also mention that you could possibly migrate it to elsewhere on the array if there is a better 'neighborhood' for it.
Hello,  I have a VNX 5300 with SAS drives, SATA drives and SSDs. Can i force a specific LUN stay only in SAS disks? Currently this LUN is in SAS and SSD drives.   Thanks.
Tiering - Force LUN on Performance Disks