I'm not sure why you are using "pg_stat_user_indexes". My original query below uses "pg_stat_all_indexes" and the schema names are joined and it does work.
SELECT n.nspname as schema,
i.relname as table,
i.indexrelname as index,
i.idx_scan,
i.idx_tup_read,
i.idx_tup_fetch,
pg_size_pretty(pg_relation_size(quote_ident(n.nspname) || '.' || quote_ident(i.relname))) AS table_size,
pg_size_pretty(pg_relation_size(quote_ident(n.nspname) || '.' || quote_ident(i.indexrelname))) AS index_size,
pg_get_indexdef(idx.indexrelid) as idx_definition
FROM pg_stat_all_indexes i
JOIN pg_class c ON (c.oid = i.relid)
JOIN pg_namespace n ON (n.oid = c.relnamespace)
JOIN pg_index idx ON (idx.indexrelid = i.indexrelid )
WHERE i.idx_scan < 200
AND NOT idx.indisprimary
AND NOT idx.indisunique
ORDER BY 1, 2, 3;