A near IR spectrometer-based analyzer attaches continuously or semi-continuously to a human subject and collects spectral measurements for determining a biological parameter in the sampled tissue, such as glucose concentration. The analyzer includes an optical system optimized to target the cutaneous layer of the sampled tissue so that interference from the adipose layer is minimized. The optical system includes at least one optical probe. Spacing between optical paths and detection fibers of each probe and between probes is optimized to minimize sampling of the adipose subcutaneous layer and to maximize collection of light backscattered from the cutaneous layer. Penetration depth is optimized by limiting range of distances between paths and detection fibers. Minimizing sampling of the adipose layer greatly reduces interference contributed by the fat band in the sample spectrum, increasing signal-to-noise ratio. Providing multiple probes also minimizes interference in the sample spectrum due to placement errors.