Limitting ranges of inputs / outputs does not work properly

Plot with some enforced limits for \Phi_D and \Phi_{cover}

Now we limit \Phi_a. It seems as if the limits for \Phi_D and \Phi_{cover} are no longer enforced and smaller values simply get the lowest values

If the lower bound of \Phi_D is only minimally increased (from 0.8 to 0.80001) everything looks fine again

possibly only one filter at a time is applied. Will have to have a look