Mac Mini - Sandisk Ultra II is not recongised?

Well I have finally managed to initialise it, however it happened because I placed it in the UPPER sata slot of the mini using my already installed 2nd HDD caddy which has a power connector adapter. This 2nd HDD kit used to house my mechanical ‘storage’ hdd, and the LOWER housed the SSD as is normal on the mini, however when I swapped them it appeared and I was able to begin installation?

I wonder if its a power issue, the old SSD that did work in lower slot is a Crucial M4, Rated +5 VDC and 2 AMPS, whereas the SanDisk is 5 & 1.6 AMPS, but to be clear I don’t understand the numbers and/or if its insignificant?

But like I said, I find it pretty bizarre as to why it won’t work in the lower slot, and although there is a threshold limit with SATA2 using a SATA3 drive, I’m getting 202MB’s Write and 252MB’s Read, which is slower than the older M4?

Thoughts?