In the attached image of the Hoffman development of Arup design, the wing is shaped in a somehow anhedral way. Why?
This plane is very interesting as it highlights a few design options.  Firstly, in seems to have neither significant dihedral nor anhedral, but it does have landing gear underneath it, lowering its CG for stability.  Being low aspect ratio, the builder probably decided to forego dihedral as cross wind gusts could make for a rolly, uncomfortable ride.  A slight sweep in the leading edges of the wing would provide some "dihedral effect" when rudder was applied.

Now for the wing itself, not albatross or eagle, we'll go flying squirrel here.  But notice how low the landing speed is.  This is a virtue of lower AR wings, though not as efficient as high AR (albatross) wings, they do stall at significantly lower speeds.  This design was also applied to the Navy "flying flapjack" and it performed well.

And thanks for the article, the ads made good reading too!