It depends on each miner. I found out that the most efficient settings is to set min voltage 0.612 and max voltage 0.618(or 0.622). I have my miners set up to min 0.614 and max 0.618.
Not sure how you do it there on your SP10, but on my SP30 running FW 2.4.21 the UI does not accept any low voltage.. This is what the UI says, and the settings must be in the range to be accepted.
I was talking about SP10. The SP30 has totally different settings!