Initial velocity won't have much effect, assuming the model converges. Boundary condition will as it'll change the overall flow rates.
Check what "length" is used for. The reference values are there to tune the coefficients to whatever you're comparing to. Hence my comments on checking the actual forces. We see many questions on here where lift & drag coefficients are not as expected, and for well meshed & converged models it's almost always poor usage of the reference values.
In 2d the model depth is (default) 1m. In theory you can change this via the reference values but it's not recommended.