Equal Operator Using Index But In Operator Not Using - postgresql

Question

I have a table with one timestamp type column and one numeric column that has combined index
table leads
(
DISPLAY_ID numeric(10),
REC_DATE timestamp without time zone,
SUP_ID numeric(10),
DISTANCE numeric(10),
RELAX_FLAG numeric(10)
)
"sampletable_indx1" btree ( date(REC_DATE), SUP_ID )
when I am running a query with equal ( = ) operator on both the columns, it is running fine
Sample Query 1
SELECT
COUNT(SUP_ID) COUNT,
SUM(CASE WHEN DISTANCE BETWEEN 0 AND 50 THEN 1 ELSE 0 END) CNT_50
FROM
(
SELECT
DISPLAY_ID,SUP_ID, DISTANCE
FROM
LEADS
WHERE
date(REC_DATE)=date(now())
AND SUP_ID = 30628898
AND RELAX_FLAG IN (6,7)
)a;
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=2.80..2.81 rows=1 width=16) (actual time=0.022..0.022 rows=1 loops=1)
-> Index Scan using sampletable_indx1 on LEADS (cost=0.57..2.79 rows=1 width=10) (actual time=0.021..0.022 rows=0 loops=1)
Index Cond: ((date(REC_DATE) = date(now())) AND (SUP_ID= '30628898'::numeric))
Filter: (RELAX_FLAG = ANY ('{6,7}'::numeric[]))
Planning time: 0.213 ms
Execution time: 0.070 ms
But when I run it for In operator for one of the column, it doesn't use the index properly
Sample Query 2
SELECT
COUNT(SUP_ID) COUNT,
SUM(CASE WHEN DISTANCE BETWEEN 0 AND 50 THEN 1 ELSE 0 END) CNT_50
FROM
(
SELECT
DISPLAY_ID,SUP_ID, DISTANCE
FROM
LEADS
WHERE
date(REC_DATE)=date(now())
AND SUP_ID IN (30628898, 23767294, 2888493, 58887272, 16226505, 1726042, 39068344, 10544691, 1445776, 24007105)
AND RELAX_FLAG IN (6,7)
)a;
QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=2.81..2.82 rows=1 width=16) (actual time=1065.310..1065.311 rows=1 loops=1)
-> Index Scan using sampletable_indx1 on LEADS (cost=0.57..2.80 rows=1 width=10) (actual time=88.814..1065.259 rows=11 loops=1)
Index Cond: (date(REC_DATE) = date(now()))
Filter: ((RELAX_FLAG = ANY ('{6,7}'::numeric[])) AND ( SUP_ID = ANY ('{30628898, 23767294, 2888493, 58887272, 16226505, 1726042, 39068344, 10544691, 1445776, 24007105}'::numeric[])))
Rows Removed by Filter: 680096
Planning time: 0.299 ms
Execution time: 1065.357 ms
What could be the reason for the same and how can it be solved ?