this is math, man... it's not my logic, you can't say 4% based on a subtraction of the inflation rate from 8 to 4, that's not correct
if you want real numbers then you should compare the total coins that will be less dumped(presumably 1800) with the total coins(including the mined coins) that will be dumped each day, or that are dumped each day
if for example the total coins dumped per day is 10k coins(i doubt is so high) per day for now(including the 3600 mined coins), with the halving this will lead to a reduction of almost 20%(10k-1800), which mean that the demand will go up by roughly 25%
this assuming that the demand will remain the same until halving, so even if the demand will remain the same and the price the same, with the halving alone the price will increase by 25% which mean around $360
I don't know what you mean by "total coins dumped per day". The total volume of coins traded per day is in the 100s of thousands, and a change by only 1800 per day is not going to have a noticeable daily effect, though it will have a long term effect.
traders are dumping and buying 100k per day? can you point me the source of this? i don't really care about the demand and supply but only the supply so i can compare better the reduction in the "mining supply"
if it's indeeded 100k per day than ok 1800 is nothing to that lower than 2% and will cause a 4% up in demand like you said