why do you think that the block reward halving will have this kind of effect on price?
We have the previous block halving to go by and we also have other alt coins to go by. People are invested in the network before halving and after halving they change nothing, so the price goes up since the supply is less.
Market prices incorporate information as soon as this information is available. The future supply of Bitcoin is completely transparent. All market participants are able to react now.
A price movement only happens when new information enters the market place. The halving is not new information and should therefore be reflected in the price already.
Generally, the supply of anything being cut by 50% will spike the price
I drink beer so if I am told by the brewery there will be 50% less supply of beer in the world every day after next June..... I will buy a pile of it before that...... But maybe not yet
A month or two before June I would buy it....
True, price does increase if supply decreases.
However, this price increase does happen as soon as people know about the supply situation. Your brewery told you about the 50% supply cut in 2016 on the day that Satoshi published bitcoin. Since then, no new information about bitcoin supply has entered the marketplace.