Reconstructing images from projections in fluorescence Optical Projection Tomography (OPT) is a relatively new problem requiring attention from researchers in this emerging field. There are several aspects of fluorescence OPT which require different treatment compared with non-fluorescence tomography. One significant problem, and the subject of this paper, is that fluorophores emit light isotropically and so the intensity of light captured at a microscope lens is inversely proportional to the square of the distance of the fluorophore from the focal point of the lens. Standard back-projection techniques do not account for this phenomenon and we show numerically that net effect is that fluorophores close to the centre of a body are assigned relatively low values in standard reconstructions. This is an inherent limitation of the standard back-projection method for quantitative fluorescence applications (e.g. in molecular imaging). In this paper we present a working, though computationally intensive, method to account for this, and discuss how more sophisticated (and less computationally intense) methods could be derived in the near future.