Raising the fixture was tried, PAR at the ends decreased, and the fixture was returned to its original height. It stays open because the before-and-after readings were never kept as a dataset, so the result is a recollection rather than a record.
Would raising the fixture improve end coverage?
PAR mapping showed the ends were receiving materially less light than the center. Raising a fixture spreads its beam over a wider area, so raising it is the obvious first thing to try before buying anything.
Raising the fixture would trade peak center intensity for a wider, more even field, improving the end positions.
Recorded before measuring, so it can be shown to have been wrong.
The original Solar RGB was raised and the outer positions were re-checked with the same Apogee meter, at the same positions and time of day, with no other change. This was done as a working check rather than as a formal survey, and the before-and-after readings were not preserved as a standalone dataset.
Raising the fixture reduced measured PAR at the end positions, so it was returned to its original height.
The original mounting position was retained because it appeared to give better coverage on this specific aquarium. Raising a narrow fixture over a long tank seems to lose more to spill outside the tank than it gains in spread. Because the comparison readings were not preserved as a standalone survey, this is recorded as an observation that informed a decision rather than as a documented result. The usual advice is to raise a light if the edges are dim. On this 90 cm tank under a compact pendant, it appeared to make things worse, and I have not found that tested anywhere with numbers, which is why the repeat below matters more than the recollection above.
Results describe this specific aquarium under the conditions recorded above. They are observations, not universal recommendations.