Currently increasing the input gain (IN 1/2 LEVEL) affects the gain of amp/pedal blocks. For tracking wet and dry signal simultaneously you cannot increase the gain of the DI signal without affecting tone.
Presumably amps blocks are also built for a particular input gain level as well. To much input (still in the green) and the amp block gets a digitally compressed sound.
Taking a note out of the Fractal Manual:
Except at very low settings (5% or less), input level adjustments do not affect gain levels. As you
adjust the level to the A/D converter, its output compensates accordingly, so your signal remains
exactly the same when it hits the grid and any virtual amps or effects.
An auto input gain compensation would take the clumsy guesswork out and allow for easier wet/dry tracking.