Smallest budget IEM?

[subwoofer]

I shall stand corrected on the size. The CX300-ii are bigger than I thought.
 
Here we have the Fidue A31s, the Sennheiser CX300-ii and the the Betron KS-45.
 

 
 
 
There is also an update on further use of the Betron KS-45:
 
The sound has improved with use and the ultra thin sound is fuller, but the seal must be perfect or they sound very light. This has resulted in the worst experience I have had with this type of earphone. After switching to the smallest of the dark eartips and getting the seal right, I came to take them out, and both eartips came off and stayed in my ear canal. It took some fishing with tweezers to free myself and has made me very cautious about getting a good seal. Really not happy about that.

 

[subwoofer]

OK, going back on what I said before about the A31s, I've now started using them as my regular night time IEMs. They sound very good and are showing me the old CX300ii are not terribly good (though they were great compared to earbuds).
 
The KS-45s are ICE only (In Case of Emergency) as I don't trust them not to leave their ear-tips in my ears.
 
Still open to any new ideas.