Length of the fuse and wingspan have absolutely no relationship with each other.
There's a rule of thumb that states that the wing quarter cord point and the horizontal stabilizer quarter cord point should be at least four times the cord of the wing apart. Mainly to keep the tail out of the downwash. However the length of the fuse is mire dependant on the size of the tailplane to ensure enough elevator and rudder authority.
Wing Span and Aspect Ratio are dependant on Induced Drag, Cruise Speed, and Stall Speed. Kitplanes magazine contributer Barnaby Wainfarn has a current series about the process of designing aeroplanes, called Design Process. He's up to wing design. The upcoming July 2020 issue will feature, Span and Aspect Ratio. It's very interesting. Read it if you can.
'Length and span have no relationship'
As in my earlier post, this technically is true, flying wing has no fuse ratio, F104 is way out the other side.
The technical design ratio is wing chord to fuse length, although arbitrarily stating 4:1 is a little bold.
Back in my day of designing control line stunt models, 2.5~3:1 gave a nice balance, but in real aircraft it can vary widely.
A Piper Cherokee would be around 2.5:1, a 737 might be around 4:1 and a performance sailplane would be up near 7:1 for the reasons I mentioned earlier.
It comes down to design goal criteria.