you might want to expirament with the polar pattern setting and the 4050 is very sensitive to phase angle coorelation. mic pres and cables can be a factor too as mics can have different characteristics with these variables.
what are you using as a mic pre?
here is an example of guitar at4040 using figure of 8 with a API 8mx2 vocal sm7b on M-Audio firewire 1814 stock mic pre positioned 45 deg. and 35 deg. off axis from center facing artist, spread about 3 ft from each other. sm7 on boom stand, AT4040 on a guitar stand fully extended:
willin.mp3
edit: also a/b flipping the phase of your AT4040