Greetings! I believe this topic has been around this forum, but I think that Rad is hard to get! You can get Shining, Glowing, Warm, Dim, and Cracked fire crystal can be crafted accordingly. Radiant is unable to be crafted. So Rad should drop more then shining. That's my suggestions, if you don't agree just leave it for others.
It is true, and this is how it used to be. Then Three Rings bumped it back to only start dropping at D27 and beyond (i.e., you would net about 6-12 radiants on a good run), then it was changed to start dropping at D25 and onwards.
Originally, people complained how hard it was to get shining fire crystals, however in the big scheme of things it really wasn't. You needed less, and they were easy to acquire... Now they're everywhere. I would recommend making shining fire crystals cease to drop at depths 27 and onwards, as that will make radiants feel like they drop more despite the same amount of fire crystals as now.