Looking for recent work done or current regulatory guidance(national or world wide), if any on the limitations of focusing RL transducers. Manufacturers claim different capabilities. Manafacturer "X" makes a 45° 2(8x14)mm 1.0MHz focused at 38mm FS, yet manufacturer "Y" says they cannot focus beyond 25mm FS for such a probe. Are all manufactures not bound by the same constraints? Freq., Element size, Velocity, Etc.