1. 21 = (32 - 11) => ( ( R & R ) | R & R ) | R actually gives 23 (which is good :)
2. 27 = (32 - 5) => ( R | R & R ) | R | R actually gives 29 which I alrady have.

One way to explore this space is to create a Perl script to list the resulting spread for all the expressions with a certain number of operators

I had a go at this, but precedence make is pretty aakward. (Eg, I was unsuccessful!)

I see that 9 is also missing from your list.

I'd missed that, but tit is an easy one: 18 = R & R & R | R so 9 = ( R & R & R | R ) & R. I'll add it in the OP.