PostgreSQL中btree_gist索引涉及integer和tstzrange属性查询计划的问题

对于PostgreSQL v15.2，我使用以下表定义:

   CREATE TABLE IF NOT EXISTS postgres_air_bitemp.frequent_flyer_transaction(
    frequent_flyer_transaction_key integer NOT NULL DEFAULT
    nextval('postgres_air_bitemp.frequent_flyer_transaction_frequent_flyer_transaction_key_seq'
      ::regclass),
    frequent_flyer_id integer NOT NULL,
    level text ,
    booking_leg_id integer,
    award_points integer,
    status_points integer,
    effective temporal_relationships.timeperiod NOT NULL,
    asserted temporal_relationships.timeperiod NOT NULL,
    row_created_at timestamp with time zone NOT NULL DEFAULT now(),
    CONSTRAINT frequent_flyer_transaction_pk PRIMARY KEY (frequent_flyer_transaction_key),
    CONSTRAINT frequent_flyer_transaction_frequent_flyer_id_assert_eff_excl EXCLUDE USING gist (
        effective WITH &&,
        asserted WITH &&,
        frequent_flyer_id WITH =)
    )

我看到这个查询的查询计划:

    airlines=# explain analyze select * from
    postgres_air_bitemp.frequent_flyer_transaction t 
    where frequent_flyer_id=39189 and now()<@asserted and now()<@effective;
                                           QUERY PLAN                                                                              
# ----------------------------------------------------------------------------------------------------------------------------------------------------------------------
    Bitmap Heap Scan on frequent_flyer_transaction t  (cost=4.69..87.91 rows=21 width=74) (actual time=0.097..0.099 rows=1 loops=1)
        Recheck Cond: (frequent_flyer_id = 39189)
        Filter: ((now() <@ (asserted)::tstzrange) AND (now() <@ (effective)::tstzrange))
        Heap Blocks: exact=1
        ->  Bitmap Index Scan on frequent_flyer_transaction_frequent_flyer_id_assert_eff_excl (cost=0.00..4.68 rows=21 width=0) (actual time=0.077..0.077 rows=1 loops=1)
            Index Cond: ((frequent_flyer_id = 39189) AND ((asserted)::tstzrange @> now()) AND ((effective)::tstzrange @> now()))
    Planning Time: 0.333 ms
    Execution Time: 0.172 ms
    (8 rows)

查询计划正确地使用了btree_gist索引，但随后它对由双时态时间范围过滤的frequent_flyer_id进行位图索引扫描，最后对frequent_flyer_id条件进行重新判断.为什么在初始btree_gist索引扫描之后需要执行后续步骤？

我希望看到一个查询计划，它只包含使用btree_gist索引的索引扫描.额外的步骤是必要的，因为gist索引是有损的，因此后续步骤是判断假阳性？