You are correct however that locking these additional 4.2m tokens, will reduce short-term supply and push the price upwards. But, this all evens out. Since these tokens are only locked temporarily, they will push the price down when they are unlocked in the future.
It's a question of affecting the market now or later. But do you really want to be manipulating the market at all?
What's more, a more effective way of pushing up the market price, if you really want to do this, would be to burn some unsold tokens.
If you burned say 4.2m unsold tokens, you could fulfill all tentative purchases, at June prices, locked or unlocked, and at the same time push the market price upwards (at least in the long term -- there's no telling what this would do in the short term).
The only downside is that burning tokens would reduce the amount of funds you can raise by selling these tokens in the future. But I imagine you are going to be able to raise far more than you need for you and the project going forward.