Have a look here: https://www.spacycles.co.uk/m8b0s210p0/Drivetrain/Chainrings-Spa
Plenty of smaller rings carried by both suppliers - in four and five arm pattern and in most common BCD sizes.
I'm running 135 BCD for outer and middle, inner runs on 74BCD attaches to 5 sockets on the inside of the spider. I had been looking for 135BCD 30T which is impossible!
Thanks for the advice, I rang Spa Cycles, that's when the penny dropped!
If you have a triple chainset with the appropriate front derailleur then its capacity will be around 22T. Double chainset derailleurs will have a smaller capacity.
I run a triple with 50-39-26 and a campag racing triple front derailleur 22T capacity and it works fine. On my solo I have a 44-38-25 and a shimano dura ace derailleur 15T capacity and that all so works fine.
So the capacity figure quoted by the manufacturers is a guide but not the whole truth.
If you want a big range of gears you may need to stretch to capacity of your derailleurs.
Don't forget about your rear derailleur's capacity if you change the front chainring. The total capacity of my chainset and gears is 42T but my rear derailleur is rated for 40T.
Capacity is probably based on the gears and chainset being sold at the time. Take Shimano Tiagra gears 11-32 cassette plus 50-40-30 chainset giving a capacity of 41T and low and behold the capacity of a medium cage Tiagra rear derailler is .... 41T.