I was going to post that 6 weeks was longer than I thought necessary. Then I realised that many people in the UK are on monthly pay schedules, and that 6 weeks might alleviate financial issues. Of course, you might consider that having had months to save the money, that isn't necessary. But even if you did reduce it, you couldn't go below 4 weeks IMO.
With regards to the take up, are able to determine whether US take up has dropped recently relative to the European take up? The exchange rate is not helping those on this side of the pond and I wonder how much that is affecting demand.