from my observation of the ip drip method i think the mb engineers wanted you to use the column of oil in the fuel filter because its mount is fixed and the drip tube is a fixed height when turned toward the block.all you are doing is setting the gap of the power piston just before it rises to its cylinder bore which starts the high pressure cycle and allows no more fuel to enter.if you use a higher fuel level than the top of the oil filter to set the one drop per sec then you timming will be set fast as the higher fuel level will push more fuel thru and you will have to speed up the pump setting to get the one per sec. lower the fuel level and your timming will be slow. just adding my opinion as i observed the total system.
larry perkins
72 old cars