cold-potato at L3/Chi into UU?

In Chicago, L3 appears to be routing some traffic to UU directly, but for some other UU destinations, L3 is handing-off to UU via New York:

trace from L3/Chi to (AS8015 via 701) is carried to UU via New York (edited):

1 ( 8 msec
  2 ( 20 msec
  4 ( 20 msec
  8 visi-gw.customer.ALTER.NET ( [AS701 {ALTERNET}] 32 msec

Oddly, a L3/Chi trace to the last hop above within AS701 ( enters UU immediately in Chicago, taking the shorter path to Minneapolis:

1 ( 0 msec
2 ( [AS701 {ALTERNET}] 0 msec
6 visi-gw.customer.ALTER.NET ( [AS701 {ALTERNET}] 8 msec

UU support has verified that AS8015 prefixes are advertised at UU's L3/Chi peering point; and L3 support reports this is "routing as designed". I would guess that UU requires its peers to use hot-potato routing, so I'm at a loss as to what kind of traffic engineering is being used.