In order to get depth with sharpies its worth useing two types , experiment on the bottom elevator for best effect .
Example on Gray monocote you may want to try a think black sharpie then a thin siler one over that line -or thin silver first then thin black over that .

Or you get -model master premixed for spray painting "exaust " simply take a air gun and cut about 10 -sheets of 12 by 12 card board stock poster board .
Line your sheet up where you want the line , spray with at least 12" from the plane and you will have a sharpe line and on the other side a buff -wing effect line .
Try to keep all the sharpe lines forward and the buffed lines towards the tail as they would be from the wind