There are many lighting/shadow mods on Nexus where people have gone through and moved and recalibrated lighting positions to remove many problems. However you cannot enable this and detailed shadows at the same time because the ENB renderer is not being injected. You can use just the memory patch with the speedpatchwithoutgraphics=true value in enblocal.ini. You can switch off individual ENB effects but just using the renderer causes slowdown regardless of whether all effects are disabled or not. but they can still be found in certain areas and lighting conditions.
Perhaps you know all this but I can confirm that is 'normal' behaviour.ĮNB can lessen these issues. Another is shadowdistance that can make shadows near by sharper but will not show more distant shadows and cause pop-in. The biggest setting to look at is the shadowresolution entry which is the basic quality of shadows.
It also depends on the capabilities of your system and the ini values I have provided are a sort of middle-high ground but not the highest settings as they drain enormous power for not a lot of visual gain.
Shadows in Skyrim are not great to start with and even at the 'best' settings can cause pixelation, lines, tartan patterns (like you describe) and other such anomalies.