Speed-vs-length matrix tables often carry a merged “Length Overall (m)” banner above the numeric column headers. Grid-Sight peels off the banner and binds interpolation to the leaf header row, so both author permutations below offer the sliders. Click the GS toggle, open the + on the top-left corner cell, choose Sliders, then drag either axis to interpolate — the bracketing four cells highlight live.
colspan bannerA single merged cell spans the whole header; the leaf row still carries the Speed Knots corner alongside the length headers.
rowspan corner + colspan bannerSpeed Knots spans both header rows, so the leaf row is all length headers (no corner cell) with its cells shifted right under the rowspan. This is the case that previously blocked interpolation.