Did you ever figure it out?
This one is gravure, the minisheet one is lithography.
Also, the phosphor bars on the sheet version are 'vignetted.' From Connoisseur:
Vignetted bands. Country Emblem definitives all have relatively dark backgrounds to their stamps, which made it necessary for wider than normal phosphor bands to achieve an adequate phosphor response to activate automatic sorting equipment. As a consequence, on two band stamps the phosphor encroaches over a large part of the design. In an attempt to make the edge of the phosphor bands less apparent, on all Walsall and most De La Rue printings the bands are "vignetted". The effect is that under UV they appear weaker the nearer to their inner edge as if being faded into the background. This makes the measurement of phosphor width difficult