I have the 58 mm thread f1 Noctilux. With the hood it blocks about a fifth of the 50 mm frame. E60 f1 Noctis with hood extended block slightly more, and the 0.95 asph Nocti again with hood extended blocks slightly more again.
The 0.85 is very nice with a Noctilux or 75 Summilux. But the 0.85 is more flare prone than the lower magnifications and even the MP finder flares sometimes.
Let us know what you think when you get it.
Marty