The larger the tone hole, the softer the pad needs to be to have the same effort (playing pressure) reach the tone hole surface as a smaller pad. This is simple physics. I've learned, through my magnehelic testing, that the pads held closed by springs are the ones that need this principal applied to the most. Octave pads and left hand palm pads are very easy for the spring tension to close on their small tone holes, but the high e and f# will have problems if their springs are located at the end farthest from the pad. The spring tension gets weakened through torsions and mass and often allows the pads to blow open when playing lower tones (low G blowing open high f# is very common).
As the tone holes get bigger, starting with side C , Bb, G# and continuing down, the problem increases. Low C# is almost impossible with the miserable amount of force making it from the spring near the left pinky to the tone hole and a firm felt pad with even contact all around. These all need softer pads and often stronger springs. A player can't squeeze these pads to make them seal so they actually define the playing potential of the instrument.
David