Optlasers does a good job of trying to match the beam diameters of the R,G,B diodes in their single mode units, but not perfect. I think their stuff is close enough to perfect, and this may also be close enough with single mode diodes because they probably aren't too far off, but a perfect match, i don't think it can be made. it's not just the diodes, it's the wavelength and optics, if you customised the optic focal lengths and diameters to bring the mRad or divergence of each diode to exactly match that would be part of the puzzle, but when doing that, now you don't have a combined red, green and blue of exactly the same diameters. Although, i bet for a distance, you cannot see the spreading of the different divergences and it may match well, but far out, they all separate. I don't know if it is possible to make a dichro combined R,G,B which is perfect. As you know, i'm just a hobbyist on this stuff, but that's how i have come to understand things.