Do not read too much into light transmission numbers, since this is not a test that is standardized by manufacturers as to equipment used and technique used. At this time, the only published light figures that are in anyway useful are figures on binoculars
subjected to the same test by the same tester at the same time and even, then, the figures can only tell you if one model is slightly better than the other. The figures should not be taken, literally. Then, too, the human eye is not capable of detecting differences of less than 3% in light transmission, anyway, so a model that scores 99% vesrus 97% for another is a moot point.
The biggest reason you are not getting the image brightness you want is, just as you have discovered the small exit pupil when using a 12x with a 40mm objective. Dropping down to any quality 7x42 or 8x42 with good lens coatings, like the Elite, will be an improvement and that, of course, assumes that your eyes can take advantage of the larger exit pupil. At my advanced age, for instance, the maximum exit pupil these old eyes can use is about 5 mm and that is only under totally dark conditions.