Where to place IR filter in the optical path

I basically have a camera, and I want to take the IR-blocking filter from a digital camera sensor, and use it to filter out all IR from the image-forming light. Since I'm making an extreme small-angle spotmeter, image sharpness and flare matter. My question is, does it matter, in regards to image quality, flare, and IR-blockage effectiveness, where I put the filter in the optical path? Digital cameras put the filter right over top of the CMOS sensor, but is there a reason for this? Would putting the filter several mm away from the image plane, or even right behind (or in front of) the lens, be better in terms of contrast, sharpness, flare, or IR blocking effectiveness?

why not just use a hot mirror filter? smaller sizes are available relatively inexpensively. Some earlier digicams (as well as the Leica) put it on the lens, so I would say that it really doesn't matter where in the optical chain you put it.