Cable choice for kitchen. Maximum demand and diversity
A ring circuit makes a full loop from the distribution panel through all receptacles.  What you have is two leads from the panel through all outlets.  The total combined load the circuit could support is your 18.5A * 2 = 37A.  The idea is that if you are using a device that draws 3A on the left-hand side, the next device you use would balance the load by pulling 3A from the right-hand side of the circuit.

So I do think you have sized the right cable.



Let me try to argue for the radial circuit, if you have room to do it.

Ring circuits can work but your supposed to balance receptacles around the circuit; that is, not all your receptacles should be in the first few metres of the circuit with the remain run just needed to complete the ring. If the distribution of appliances is not balanced that could lead to the load not balanced and one section of the ring with a heavier load than it should be carrying, heating your mains until it started a fire.  

A fault in the mains could lead to one of the leads from the panel supporting the entire load of the circuit, suddenly you have the 37A supported on a radial circuit, with a 30A breaker, and a cable rated for only 18.5A.  Again, overheating and fire.  A fault in a ring circuit may not be all that noticeable.

With a radial circuit, if there is a fault.  The most likely result is a blown breaker or the circuit stop working.

There are some arguments about electrical noise induced by full ring.  Not sure what the reality of this issue is.