VF stands for forward voltage, but a higher forward voltage doesn't necessarily mean a higher forward current. You'll see a VF value and an If value on the certificate of manufacture of any low-power LED. Regardless of the VF value (generally 1.8V-2.4V for red, yellow, yellow-green, and orange; 3.0V-3.6V for white, blue, and emerald green), the If value is always 20mA.
These two values are interdependent. For example, with two white LEDs, one rated at 3.0V and 20mA, and the other at 3.4V and 20mA, it means that if you apply 3.0V to the first LED, the current flowing through it will be the normal rated current of 20mA. However, for the second LED, you need to apply 3.4V to achieve the same 20mA current.
Here, Vf and If are not directly proportional; however, comparing a yellow LED and a white LED, for example, if the yellow LED's voltage is 2.0V and the white LED's voltage is 3.3V, the current flowing through them is the same—20mA—both. In this case, Vf and If are not directly proportional.
Therefore, Vf and If are only absolutely proportional when referring specifically to the same LED. When using it, regardless of the actual Vf value, as long as the current flowing through all LEDs is controlled to be 20mA, it's fine.