The Focal 948 are slightly more efficient over the 936's, but cabinet volume in relation to surface radiation area is a bit less on the 948 as compared to the 936. The main reasoning to not going further is the efficiency for the mid and tweeter drivers are not any more capable in the 948 or 936. At 92db vs 92.5db, either design is at the upper end efficiency for typical cones and domes without resorting to horn loading or other techniques for the mid and tweeter. Focal hit the limit of those drivers first and in the bass could instead be tuned for deeper response in port tuning and lower distortion.
A good deal of other lines out there do gain significant efficiency in larger models as they shelve their mid/tweeter drivers down in level in the crossover in smaller designs as compared to larger. The flax cones are pretty light and achieve output similar to coated paper drivers, but obviously they have their own set of compromises.
Now the line array theory isn't entirely effective in the 936 as the driver symmetry goes off in the upper end of their pass band. Since its pretty low in level, the audibility isn't high and is given as acceptable in a design at this price point. Agreeably, this has more to do with the more complex bass driver arrangement in the 936 over the other models in the line. To make that coupling work really well, you require high constancy in driver and operating environment, which some designs to practice to good effect.
A good deal of other lines out there do gain significant efficiency in larger models as they shelve their mid/tweeter drivers down in level in the crossover in smaller designs as compared to larger. The flax cones are pretty light and achieve output similar to coated paper drivers, but obviously they have their own set of compromises.
Now the line array theory isn't entirely effective in the 936 as the driver symmetry goes off in the upper end of their pass band. Since its pretty low in level, the audibility isn't high and is given as acceptable in a design at this price point. Agreeably, this has more to do with the more complex bass driver arrangement in the 936 over the other models in the line. To make that coupling work really well, you require high constancy in driver and operating environment, which some designs to practice to good effect.