Bristol 4d To Pay

Here's an item I acquired at the recent S&DPHG meeting in Chard.  It is a thin wrappper and looks like a newspaper wrapper.  It bears an assortment of handstamps, a manuscript endorsement and postage due.

In particular it is endorsed "Contains Letter" so the first question that occurred to me was whether it was charged extra because the Post Office had found a letter inside something sent as a newpaper or printed matter.

The conclusion I came to was that the wrapper must have been posted as Printed Matter (2d for 4-6 oz.) and the letter or just a written message discovered inside.  The handstamp "More to Pay / above 6 oz / 134" doesn't exactly fit any scenario if it was taken literally as indicating that the wrapper was over-weight (a postage due of at least 5d would be required).  I've assumed that it was there to indicate the actual weight limit being charged (6 oz.) which does fit with both the initial franking of 2d under the Printed Matter rate and the 4d postage due when it was charged at the Inland Letter rate.

Please let me know if you think my conclusions are wrong !