This paper presents experimental evaluation of ammonia receiver geometries with a 9 m2 dish concentrator. The experiments involved varying the geometric arrangement of reactor tubes in a thermochemical reactor built from a series of tubes arranged in a conical shape inside a cavity receiver. Differences in conical arrangement were found to affect the efficiency of energy conversion. The solar-to-chemical efficiency gain obtained by varying the receiver geometry was up to 7% absolute. From this, it is apparent that geometric optimizations are worth pursuing since the resulting efficiency gains are achieved with no increase in costs of manufacture for receivers. The experimental results and methodology can be used when developing receivers for larger dish concentrators, such as the second generation 500 m2 dish concentrator developed at the Australian National University.