While the alpha of the texture data is not used at all (replaced with blue using the view swizzle), still make the shader code state the intention more explicitly if the format is decompressed for use as signed. Unsigned 1.0 is 0xFF, while signed 1.0 is 0x7F.
The original multiplication was likely added early during the development of generic resolution scaling. Before generic resolution scaling, invocations were done for unscaled guest blocks, now they're done for scaled blocks, so with 3x1 scaling, an invocation for 8 blocks writes 8 host blocks, not 24.
