Boss VF-1 Effect Processor

Hi,
I recently bought a VF-1 second hand and while testing I noticed a 
(in my opinion) strange behaviour: When I switch the input 
sensitivity switch from -20 to +4 the meters correctly show the lower 
input level but overall the signal gets louder (in some patches much 
louder!). It makes no difference using the High-Z or the rear inputs, 
the signal gets boostet up.
Is this the normal behaviour of the VF-1 or did I bought a faulty 
unit?
Another thing that annoys me that the +4-setting is much better 
sounding for distortions, but nearly useless for input-triggered FX 
like Phasers or Wha's.
Hope someone can clear me up.
Thanks,
Phil