Like many/most, I cannot use the B17 with my bars below the saddle. In fact, I prefer the bars 1-2 cm. above the saddle with a B17.
And I am another one who finds that the angle is critical. As others have noted, the "hammock" shape tends to slide your bits onto the nose if the rear of the saddle is not relatively level - which means that the nose must be up in the air. But if the nose is too far up, it'll jab into your bits too. I have to have a two-bolt micro-adjust seatpost to get it right. On the first ride I'll be on and off the bike half a dozen times getting the adjustment exactly right.
Lacing the saddle (or buying one already laced) reduces the amount of "hammock" while riding and helps me quite a bit.
The cutouts available on the the B17 "Imperial" are very helpful for me too. On older versions I have done the cutting myself.
So for me, the B17 is a heavy, difficult saddle with a big price tag - and I use them almost exclusively, because nothing else is as comfortable for me.