Chard or Bath "MORE TO PAY / OVER OZ" cover from 1865

The cover below is addressed to Shaftesbury with an indistinct barred numeral cancel, a "MORE TO PAY / OVER ½ OZ" cachet, and a manuscript charge of "2d" with initials.

 On the reverse the envelope has single ring handstamps from Chard (April 4th 1865), Bath (April 5th 1865) and Shaftesbury (April 5th 1865).

Based on the backstamps, it would appear that the envelope originated in Chard, and went to Shaftesbury via Bath.   

Question 1:  Why would the envelope go via Bath, rather than the direct route via Yeovil and Sherborne ?

Question 2:  Where was the "MORE TO PAY / OVER   OZ" cachet applied ?

No such cachet is yet recorded used at Chard, but a very similar cachet was issued to Bath on the 20th September 1855, with a proof in the Steel Impression Book.  This cachet has been recorded in use from 1857 to 1861.  This example matches well with other examples.

Normally one would expect a More-To-Pay cachet to be applied at the originating Post Office, so at Chard.

However if the envelope was misrouted to Bath, it is likely that the envelope was examined while it was being re-sorted and found to be overweight;  in this case the More-To-Pay cachet could reasonably originate in Bath.

My conclusion:  The envelope probably went via Bath because it was mis-sorted at Chard and put in the wrong bag.  It is then probable that the envelope was picked out at Bath when it was re-sorted and the More-To-Pay cachet applied there.