Yes, cowling shadowing is a real issue and worse than you would expect for Amps with your panel type. Shading like that eats into your available roof real estate and hurts all types of panels.
On a clear day, there is very little light dispersion and tilting rules. Cloudy days, there is less obvious tilting effect and sometimes more insolation can be had tilting towards the bulk of a brighter sky which may not be perpendicular to the sun. Trees and mottled shade can have a similar effect. These factors can dictate which type of panels are best.
At your latitude, you may find that flat is optimal and more Watts is easier.
HTH;
John
