How did the Soviets allocate radios to tanks?

(In reference to the Chieftain special on Soviet light vehicles) It’s interesting to see how different tank models would be given radios at higher or lower rates to each other, for example half of BT-7s had radios while only a quarter of BT-5s had them. How did the Soviet Union decide which units received radios and which did not? Was it by model (e.g. BT-7s get priority), by unit (e.g. border units get priority), or something entirely different? Love the channel BTW.