BGP path prepend / route selection

[Amadeus]

Dear list,
can you explain why the following route (0.0.0.0/0) is selected to go via
as403, as as4057 clearly displays the shortest path here?
As you can see I have used bgp_path.prepend() 3x on as403 for its own ASN.
Thanks, Amadeus
bird> show route for 0.0.0.0/0 table ffc all
0.0.0.0/0          via 169.254.40.3 on ffc403 [as403 14:38] * (150)
[AS403i]
 Type: BGP unicast univ
 BGP.origin: IGP
 BGP.as_path: 403 403 403 403
 BGP.next_hop: 169.254.40.3
 BGP.local_pref: 100
                   via 169.254.40.64 on ffc4064 [as4064 14:32] (100)
[AS4057i]
 Type: BGP unicast univ
 BGP.origin: IGP
 BGP.as_path: 4064 40120 4057
 BGP.next_hop: 169.254.40.64
 BGP.local_pref: 100
                   via 169.254.40.57 on ffc4057 [as4057 Oct14] (100)
[AS4057i]
 Type: BGP unicast univ
 BGP.origin: IGP
 BGP.as_path: 4057
 BGP.next_hop: 169.254.40.57
 BGP.local_pref: 100
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