Isn't this idea similar to forbidding selfvotes? If you can't do it with one account, you can do it with another one or multiple ones.

Moreover, how would you define the cap threshold? Is the cap of HP towards one proposal?

Would splitting the total HP usable for proposal voting be better utilized if it was split amongst all voted proposals in some ratio?

Could using logarithmic vote scale be a better way of dealing with similar issues?

Sorry for the unanswered questions. However, I feel I see people reacting similarly but didn't see any reasonable solution backed by more than opinions.