Sparge Temp and efficiency

We fly sparge using a gravity system and a basic ring shaped sparge arm. We first drain the mash until the level is one inch above the grain bed and begin our sparge. We use 170 degree water to sparge but when it mixes with the ~150 degree water from the mash the temperature obviously drops significantly. Should we be hitting it with much hotter water to bring the temperature up as we begin the sparge and then continue the sparge with 170 degree water. I guess this would be like a mashout, but seems like a lot of water to add to bring all the mash water up to that temperature. Should we be draining the mash more? Our efficiencies on our first 2 all grain batches have been around 70% using milled malts from morebeer and homebrewersoutpost. What are some other ways to increase efficiences?

170 is something of a magic number for mashing. If you get higher than that, you solubilize tannins and can have astringent beer. The lower the temp, though, the less effectively you're pulling sugar out of the mash. Ideally, you'd keep your sparge right at 170F. This means adding water above 170F.

I'm no fly sparger, but what you describe sounds right as far as volume goes.