Boost_factor doesn't work under functions

Hello. i wrote a query for scoring integer field.
but i faced with a problem while giving a weight to my script query(decay_function)
I read some docs(below). i found boost_factor( under ES 1.3. i'm using 1.3 version)

but it is not multiplying a weight but changing script score to just a weight that i given (description : "static boost factor")
I'm wondering it is working well or not? qeury is below

"exp": {
"read_cnt": {
"origin": "2478",
"scale": "500",
"offset": "0",
"decay": 0.9
"boost_factor": 0.6