I have a Moeck Rottenburgh (pearwood) alto and I have the same problem with the high F. It’s a hit or miss which is quite frustrating. It’s much easier for me to consistently hit that note on the pearwood Mollenhauer Denner or plastic recorders like Aulos 709BW (Haka) or the Dolmetsch plastic Nova. But overall I much prefer the tone of the Moeck to the Mollenhauer. The low register on the Moeck Rottenburgh is quite strong. The Mollenhauer, on the other hand, has a stronger high register but I am less than impressed with the tone that I can produce on it. I am much more satisfied with how I sound on the Moeck, except for the high F unfortunately.