You pretty much are going to the get the same advice over and over. Get two hides. Make sure that each hide is identical. I like to make sure the hides are mirror images of eachother. Then make sure you have a proper temperature gradient. If you have that and your snake chooses to be on the cold side then that's where the snake wants to be. I will say that sometimes if I see my BP is on the cold side and she has just eaten or my ambient temps are a bit cold and think its just odd, I will check for urates or fecal matter again. Sometimes I find I missed some waste that needs to be cleaned. Sometimes she is just needing to cool down a bit. It might not hurt to clean the substrate under the hides just to make sure your snake is not making the choice based on something other than temp.