I've already considered the ENG 1-90, but a pair of them stacked would be taller than my midhorn design unless they were each trimmed flat on one side and adhesed together. With a pair per box plus modifications, that would become very cost prohibitive for a 3- or 4-box line array (per side)!

The design is already a bit large so I'm hesitant to enlarge the mouth unless it's necessary, and I'm afraid to make it shorter due to increasing diffractive effects. Decisions, decisions!