PROBLEM: Custom block spawn

Hi, i made custom block (mc 1.12.2, mcreator 2019.5):

- block base: default basic block

- transparency type: solid

- materiał: rock

- Dimensions to generate in: Surface 

- blocks this ore can replace: none

- restriction biomes: none

- average amount of ore groups per chunk: 1

- average number of ores in a group: 1

- minimal generation heigh: 25

- maximal generation height: 50

Problem is my block can spawn randomly in big groups in all height. Can anyone help?