The best performing HTS conductors are available in the form of thin tapes with operating current in the range of 200 A at the operating conditions. To realize conductors with high current carrying capability, in the range of several tens of kA, a large number of tapes must be assembled in a cable. The conventional stranding methods for round conductors are not applicable to thin tapes. CRPP has developed an assembly concept based on twisted stacks of tapes soldered into a copper profile. The ability to withstand bending and torsion strain is the main issue for the design of a high current flat cable based on twisted stacks of HTS tapes. An analytical mechanical model was developed and validated with the results of measurements. Parametric analyses are used to select the optimum layout for the first full size prototype of the coming HTS conductor for fusion. Various configurations of the cable are presented and compared, paying attention in particular to the strain acting in the tape. The chosen set of cable parameters satisfies electromechanical limitations and provides feasibility of strand winding.