Greg, good eye, the blade is 2-1/8"...I am using a magnet taken from the innards of a discarded hard-drive.
The magnets found in them are very strong, about the size of a quarter, and about the same thickness.
This blade will not fall out. It takes more pull to dislodge it from this magnet, than it would take if the welt had good built-in retentions feature.
The lanyard is not adjustable...it's there to help in extracting the knife from the sheath, so there's plenty lanyard there.