Actually in a proper testudo you overlap the "roof" shields to an extent, so it shouldn't be much of a problem if done properly (which the image doesn't do to be fair).
And it propably makes sense to have slightly larger standardized holes so that every one also fits any special weapon.
I find those gun slots too large for just simple bolters. And they would prove a liability for the roof of a testudo.
Actually in a proper testudo you overlap the "roof" shields to an extent, so it shouldn't be much of a problem if done properly (which the image doesn't do to be fair).
And it propably makes sense to have slightly larger standardized holes so that every one also fits any special weapon.
[inserts fortifying the position joke here]