BPs rarely soak if their husbandry is perfect and they are healthy. They don't really soak to prepare for sheds either. In fact, bathing will ruin an oncoming shed.
You might get an odd BP once in a blue moon that may soak for the heck of it, but its not common.
A BP will soak if:
1) they have mites
Or
2) your temperature is actually incorrect and is hotter than you think and the snake is trying to cool down.
How are you measuring your temps and humidity? And where in the enclosure is it measuring temps?
From what you said, your humidity is a little on the low side if its 45%. It should be more towards 60%. But its not a huge deal unless they going into shed.
Sent from my DROID RAZR using Tapatalk 2