Change the GR6J exponential reservoir representation
For the exponential reservoir, it is a saturation deficit.
By default, it would be better to put a level below the straight line meaning zero (which could appear as a dotted line) and put a single arrow (rather than double) going from zero to the level.
And X6 is not a capacity but an emptying coefficient, so maybe put it rather at the level of the tank outlet line (I admit, the schematic of Raji's article was not very good in terms of precision!).