ppl with high frequency loss and who still have good low frequency hearing, need larger vents or even open vents. This allows hearing the low frequencies naturally through the open (or at least big/not small) vents
ppl with a hearing loss that incudes loss of hearing in low frequencies need a more occluded fit (with little or no vents) to prevent the low frequency sounds from just leaking out of your ears before your eardrums can process the Bass sound waves from your speakers/receivers
