The turbo on the 1070s are kinda weird, when I had mine it boost up to 2050mhz and hang there for a little while and then drop to 2000mhz even when temps are around 50C, It never stayed where I set it. That is until I did the shunt mod, then when I put it at 2050mhz it didn't move from it because the mod tricks the card into thinking its drawing less power.
I think when other parts of the card gets used, it distributes power to other places thats needed and has to downclock so it wont pass a set power limit that Nvidia sets. I mean I could be wrong, I don't really deal or pay much attention to the inner working of the graphics card. I do know the hotter they run, the less it clocks its self up. And if a game doesn't use the GPU to its full potential, it may not even clock up fully.