I've only had one instance where my DI unit actually showed what was obviously "fish" around wood cover :
Most of the rest of the times all I see are small white dots, that may or may not be fish.
But, to answer your question .... yes, I do fish the cover, just to be sure. I'm also going to make it a habit to mark a waypoint on newly discovered cover, so that I can come back to that spot later or on subsequent trips, and check it out ... which, unfortunately (for me) I did not do when taking the screenshot pictured above.