VTOL HSI lineup needles are based on a set distance away from the LOC centerline, this means that no matter the distance, the line stays the same sensitivity.
IRL, the needles are based on a set number of degrees off centerline. This makes it so that as you approach 0 DME, the needles become much more sensitive and reactive, making it much easier to gauge your position, as each mark represents 2 degrees off centerline. I believe this also applies to the glideslope, but I'm unsure.
This link is a good tool to visualize it https://www.luizmonteiro.com/learning_hsi_sim.aspx
#HSI needles rework
silver lodge
silver lodge
someone brought up that the notches can vary in sensitivity based on the approach, i think 2 degrees still makes the most sense for VTOL