There’s third way which requires basic math skills.
- increase max amount a bit to make this easier
- subtract your current blood shards from your max amount (for example 1430 - 1256)
- find correct GR tier from chart below so that you get above amount you want but still stay below your max amount.
https://us.forums.blizzard.com/en/d3/t/greater-rift-drop-rate/15445/6