Why cannot the iPhone bluetooth volume full soft?

Experience with iPhone SE version 13.1.3 with Shure SE535LTD earphones with BT2-EFS.

And Bluetooth in general, under (or above from 0 volume) a percent of the slider the volume is completely silence, the the volume start suddenly, to a at my opinion high volume.

Setting Spotify on Soft volume and the EQ sliders to 0 helping the volume set lower, but sommetimes even with that i will a lower volume.