A shape-sensing system comprising: a multi-core optical fiber (108, 300) having embedded therein: a central waveguide core (200, 302) placed along a center axis of the optical fiber (108, 300); and at least four helically wound peripheral waveguide cores (202, 304, 306) placed at fixed radial distances from the center axis, a value of a first radial distance of the fixed radial distances differing from a value of at least a second radial distance of the fixed radial distances; and a plurality of interrogators coupled to the central and the at least four peripheral waveguide cores (200, 202, 302, 304, 306); at an output of the plurality of interrogators, acquisition electronics configured to measure signals resulting at least in part from light reflected in the central and at least four peripheral waveguide cores (200, 202, 302, 304, 306) as the light is swept across a tuning range; and a processing facility configured to compute, for each of a plurality of positions along the optical fiber (108, 300), one or more strain metrics from the signals associated with the central waveguide core (200, 302) and at least three peripheral waveguide cores selected among the at least four peripheral waveguide cores (202, 304, 306) based on the fixed radial distances of the at least four peripheral waveguide cores (202, 304, 306) from the center axis in conjunction with a determination of whether the at least four peripheral waveguide cores (202, 304, 306) have strained, at that position along the fiber (108, 300), out of a range of strains measurable within the tuning range. a multi-core optical fiber (108, 300) having embedded therein: a central waveguide core (200, 302) placed along a center axis of the optical fiber (108, 300); and at least four helically wound peripheral waveguide cores (202, 304, 306) placed at fixed radial distances from the center axis, a value of a first radial distance of the fixed radial distances differing from a value of at least a second radial distance of the fixed radial distances; and a central waveguide core (200, 302) placed along a center axis of the optical fiber (108, 300); and at least four helically wound peripheral waveguide cores (202, 304, 306) placed at fixed radial distances from the center axis, a value of a first radial distance of the fixed radial distances differing from a value of at least a second radial distance of the fixed radial distances; and a plurality of interrogators coupled to the central and the at least four peripheral waveguide cores (200, 202, 302, 304, 306); at an output of the plurality of interrogators, acquisition electronics configured to measure signals resulting at least in part from light reflected in the central and at least four peripheral waveguide cores (200, 202, 302, 304, 306) as the light is swept across a tuning range; and a processing facility configured to compute, for each of a plurality of positions along the optical fiber (108, 300), one or more strain metrics from the signals associated with the central waveguide core (200, 302) and at least three peripheral waveguide cores selected among the at least four peripheral waveguide cores (202, 304, 306) based on the fixed radial distances of the at least four peripheral waveguide cores (202, 304, 306) from the center axis in conjunction with a determination of whether the at least four peripheral waveguide cores (202, 304, 306) have strained, at that position along the fiber (108, 300), out of a range of strains measurable within the tuning range.