  The effect of the pulse envelope on electron-positron pair creation in a
circularly-polarised laser pulse is investigated. Interference on the length
scale of the pulse envelope, and smoothness of the pulse edges are found to
influence the pair spectrum. A toy model of a flat-top pulse is used to
identify pulse envelope effects inaccessible to local approaches. Broadening of
channel openings and a widening of the energy and transverse momentum
distribution of the pair are found to receive contributions that are below the
local harmonic threshold. By comparing pair yields in a flat-top, sine-squared
and Gaussian pulse, a link between pulse shape and photon-polarised
Breit-Wheeler is found. In the transverse momentum distribution, a signal of
pulse envelope interference is found in an azimuthal asymmetry, which appears
in intense fields and persists in long pulses.
