File size anomaly with radio downloads

[Budgie]

Dolphin reports the downloaded file size of The News Quiz Series 79 
Episode 1 to be 10.5 MiB but Episodes 2 to 8 to be 27.8 MiB.

I picked this up during trouble shooting because Episode 1 does not play 
through my normal renderer when served by Minimserver server.  The other 
Episodes do play from this server.

Episode 1 plays just fine using NFS share and VLC so file is complete, 
but before I dig further into why the first file does not play, I would 
like to understand why the file for the first episode is so much 
smaller.  How can I find this out.

Since for spoken word, as opposed to opera, the smaller file sounds 
fine, what can I do to reduce the file size for the larger files I have 
now and what prefs should I be using for future spoken word downloads to 
keep file sizes down?

Budgie