It’s pretty clear why they chose the 105%. If you can take supply off the market all the way up to (5%) more than the market price, that should drive up the market price. If successful, that allows the price to be driven up again off the new higher price, etc, until we have reinflated the bubble.
It may only be 5% at a time, but this is yet another measure designed to ultimately boost home prices so they stay in the stratosphere, and maybe even go higher than they are today.