If you have 50 HP staked and you stake 50 HIVE, you are getting double the VESTS. Because the voting power depends on the used VESTS, you get 50% in this case.
If you powered up 100 HIVE (for the 50HP case and 0% upvote power), you would have moved to 66% Upvote power, and so on...
Imagine like this, if you have X HP, the % of voting power is relative to that HP... so if you add more HP, that percentage changes accordingly.
If you have 50 HP staked and you stake 50 HIVE, you are getting double the VESTS. Because the voting power depends on the used VESTS, you get 50% in this case.
If you powered up 100 HIVE (for the 50HP case and 0% upvote power), you would have moved to 66% Upvote power, and so on...
Imagine like this, if you have X HP, the % of voting power is relative to that HP... so if you add more HP, that percentage changes accordingly.