The syntax for aggregates and window functions is confusing, this does not work,

SELECT (max(x)+5) OVER () FROM generate_series(1,10) AS t(x);

While this works

SELECT 5+max(x) OVER () FROM generate_series(1,10) AS t(x);

That's fine if the operator is commutative, but I'm trying to divide an interval by seconds (in my specific case though I worked around it). Is there anyway to simplify this.

SELECT (max(x)/5) OVER () FROM generate_series(1,10) AS t(x);

So another encapsulating query is not needed? Is this a PostgreSQL thing, or a SQL thing? Is there a way to disambiguate the query?