Which +2 extensions are flush with a 18" (not 18.5") barrel?

[manbearpig]

does the DLASK +2 extension line up flush with the 18.5" barrels, or with the 18" barrels?

i need a +2 mag extension for an 18" 870P barrel, and would prefer if it lined up flush. i hate it when theyre not flush

 

[ARWEN ACE]

The Vang Comp ones are flush.