A note on mounting a T 20, the cheapest and very workable way I have found is a 1" QD Weaver style scope ring, but it has to be a high ring for the bezel of the light to clear the lens cover on the Photon XT 4.6.
Also, a ring with a smaller "T" shape QD feature works best, some levers on QD rings will rub on the scope. I had a spare set of both 1" and 30mm low Leupold QD rings and another brand of medium. The levers barely rubbed. The 1" didn't provide sufficient clearence for the bezel, the 30mm mounted at the end of the light on the tail piece allowed just sufficient clearance, but every time I zoomed the light's beam I unscrewed the tail piece. I finally ordered a cheap set of high 1" QD rings - so cheap I wouldn't trust them to hold zero on a scope, but they work fine on the light.
BTW, I use QD rings so I can remove the light from the scope, which is set up in a Burris PERP one piece mount, so I can store the scope in the original case, along with the light, spare batteries for both, etc. The light and spares fit nicely in a soft sunglasses case, which fits alongside the scope in it's case.
FWIW, I find the view through the scope much clearer with the T 20 than with the on board illuminator. My T 20 has only one power setting, but the zoom feature works well enough adjusting the amount of IR light. Zoomed out to full flood and the amount of IR light isn't overwhelming at close range, zoomed tight it is plenty sufficient well beyond 100yds. Perhaps the only drawback to a one power setting T 20 is that if you are on the ground in an area with some tall grass or brush you will get washout from too much light at close range. A lower power setting and more zoom would probably succeed in cutting down the washout while still providing sufficient light at the target.
Also FWIW, I was able to confirm zero the other day with the center piece out of the scope cover, I just used the knob to reduce screen brightness. Of course, after I was done I found the centerpiece with the pinhole...
JPK