factoring receivables

i have memorized like as follows:
if customer paying pattern changes after given to factor,
suppose receivable day reduced to 30days from 45 days.
cost side we calculate
sales*30/365*extra interest
and on benefit side,
redn in receivables *overdraft interest.

where the customer paying pattern didnt change
cost side
sales*45/365*factor interest
and on benefit side
we dont have redn in receivables..

i just want to confirm that ,
thanks