Hi,
first of all it depends on the size of your shop. As far as I remember (my shop is toooo small

), the optimum size is 100 qm to start with the advertising.
Then there are 40,000 units which can be put into one shop. More won't have any affect on the period of sale.
So, 370 is much to less to have any effect... I could imagine that you will see a decrease of the time only from aprox. 1,000 on, but I do not know for sure...
Regards,
Tycoon