If you think about diffusion it makes sense. There’s two aspects you should think about, the radius of the projected beam, and the blur radius that the lens generates. A properly focused smooth TIR will produce a beam and blur radius with a diameter proportional to the emission surface size, but if you add pebbling/diffusion layer to the same lens you will get increased blur radius proportional to the roughness of the surface.
Here we have two examples to illustrate the beam diameter and blur diameter, on the left is the stock TS10, on the right is my modified single LED TS10.
Adding pebbling or a diffusion layer is the equivalent of making a gaussian blur, the diffusion radius will get larger, and it will get to a point where the diffusion radius is equal or larger than the original beam radius, so the diffusion will go all the way through the beam, resulting in reduced beam intensity. One way to gain intensity back is by enlarging the light emission surface, while keeping the same intensity, so the beam radius gets back to being larger than the blur radius. You can still regain some of the intensity by enlarging the emission surface at a reduced intensity, but only at some extent. If you go all the way and increase diffusion to the maximum the candela will depend only on the lumen output of the light source, no matter how intense or small the source is. Maybe swapping to a SFT40 will result in increased candela, maybe not, further testing is necessary, but it’s for sure a not ideal solution for this problem (too much heat, emitter will be underused on this host).
The best approach for gaining intensity in this case might be as simple as removing the pebbling, which is the whole point of the discussion. Going for an even smaller emission surface while keeping the pebbling will result in reduced candela, despite the increase in emission surface intensity. Unexpected beam artifacts might appear by removing the pebbling though.
Or, maybe, making the bezel longer to accommodate proper smooth optics, that won’t hurt either. To my eyes the increased length brings a new character for the device. A good one for sure.