Getting as much information prior to an assessment is key to making the whole experience much simpler and comfortable.
The X-seam is a key measurement for determining the leg length and necessary chain adjustment for recumbent and semi-recumbent cycles and tricycles.
Where it is not convenient to take the measurement with the client sitting against a wall, you may need to use a fabric measuring tape and obtain this measurement whilst they are seated in their/your wheelchair.
For accuracy please ensure that the client is not wearing baggy garments. Create just a few degrees of bend at the knee and have the toes pointing upwards as much as you can. If possible take the measurement with the footwear the client intends to use for cycling.