Ok I will try to speak from a keepers aspect and will try and help you understand some of the reasons why you Ball is doing what it is doing
First
Or be soaking from time to time to help keep it hydrated. Balls drink very little water when they drink but like all reptiles do keep hydrated through their skin. So lower humidity can cause a ball to soak to try and get hydrated, its faster than drinking.
First this is a danger risk to you snake it can become burned if the light get to hot and the snake comes in contact with it. Second lights dry out the environment they are exposed to having kept balls in tanks for many years I can attest to the fact that using lights outside the tank to heat is fine it just means more work for the keep to try and maintain the RH (relative humidity) that is needed.
Thats not to say it wont. My suggestion would be place the light outside the tank because any responsible pet owner would not want to knowingly place there pet in a situation where they might get hurt or even die.
Because they were designed to live in plains of Africa where food and water can be scarce. I have see Balls live through not eating for 6+ months and come through just fine.
No one here is trying to "Tell" you what to do. You asked why your ball python is soaking these are some possibilities take them and do with them as you will.
But remember you wouldn't go to a mechanic and say "my car is acting funny can you tell me what it is?" then when the mechanic come back and says "Oh it your whatever hose" would you look at him and say "that can be I've had this car for 5 months and never had a problem with that so it can't be that".