This article provides one expected behavior that SRX prefers the next hop of ARP entry over longest matching prefix route of RE routing table.

+* --- Topology --- *+

SRX_1(1.1.1.1/24)--xe-0/0/0--(1.1.1.2/24)SRX_2
 

+* --- Adding one longer matching prefix route on SRX_1 --- *+

set routing-options static route 1.1.1.0/26 next-hop xe-0/0/1.0
 

SRX_1# run show arp | match 1.1.1.2 
00:21:59:80:3c:00 1.1.1.2     1.1.1.2          xe-0/0/0.0       none <<< there has ARP entry for 1.1.1.2

SRX_1# run show route 1.1.1.2 
inet.0: 12 destinations, 12 routes (12 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
1.1.1.0/26     *[Static/5] 00:43:28
               > via xe-0/0/1.0                                      <<< the next-hop is via interface xe-0/0/1.0 from RE routing table 

SRX_1# run show route forwarding-table destination 1.1.1.2 
Routing table: default.inet
Internet:
Destination    Type RtRef Next hop      Type Index  NhRef Netif
1.1.1.2/32     dest   0 0:21:59:80:3c:0  ucst   577   1 xe-0/0/0.0  <<< SRX forwarding table will use interface xe-0/0/0.0 as next-hop

ARP entry is not known to RE route table, after adding "exact" option, there will be no route information for 1.1.1.2 displayed as below:

SRX_1# run show route 1.1.1.2 exact 

For SRX forwarding table, the exact matching ARP entry is available on it.

This is one expected behavior.