The wavelength bypass can be controlled by the thickness and composition of the coating for each window and by the amount of space between windows. The manufacturer must monitor the production of each window to assure the proper performance of the filter. If you own an LPF, try holding it to a light and tilt it. You'll see it changing colours. This is caused by the varying length of light path through each window.
Most manufacturers add an anti-glare coating to prevent ghost images and increase image sharpness.
When using an LPF, it's critically important to keep it perpendicular to the optical axis of your telescope. This difference is extremely slight,however, and probably not detectable to the human eye. These are the colours of light your filter transmits and those that deep-sky objects emit. Deep-sky objects also emit red light. The dark-adapted human eye cannot see this red light , but some LPF's transmit red light for photography.