Hey, thanks for chiming in!
When using an inverse panel to modulate a sequence of normal panels, the diffusion angles need to cancel out.
Here is a drawing with a 1D normal panel shown in green with an inverse panel super-imposed over it in brown. The scatter drawing shows that the diffusion angles are indeed opposite to each other as required.
Now the situation using our proposed inverse panel, shown in purple.
The diffusion angles are no longer all opposite, meaning that the modulation will be unable to produce the even lobes we are looking for.
An analysis using huygens drawings brings out the same result.
From this, I would say that for panels used in normal / inverse pairings, the substitution should not be allowed. Where an inverse panel is used in a stand-alone situation, substitution is still a possibility.
For 1D panels, an inverse is generally only introduced as part of a modulation scheme, so I would not look at introducing a change there.
When it comes to 2D panels, the situation seems to be the opposite. I've not seen any examples of pairings. In fact the only advice comes from RPG, who advise using a random orientation for their 2D panels. In this situation I'm thinking of treating all 2D inverses as stand-alone panels, and am considering using the substitution.
As for the depth savings, you need to look at the drawings carefully. The QRDude screenshot in the first post shows a panel that has no zero-depth wells and the total height is 7 depth units - including the fins, which sit up 1 depth unit above the tallest block.
The second posting shows the panel if substitution is used. There is now a block with zero depth but no longer any with full depth. The entire bottom layer is disgarded, and the total height is now 6 depth units.
This depth saving is the major advantage to using the substitution. A smaller advantage is that it becomes easy to see the orientation of the panel when multiples are used in an array. A final advantage, and one that is not much use to us DIY'ers, is that the single zero-depth well is the perfect spot to place your manufacturer's logo..