The difficulty level adjustment algorithm does not prevent a miner from mining blocks at a very fast rate, it only tries to adjust the difficulty over time to try and maintain 6 blocks per hour. It will never get an exact 6 blocks per hour.

The multiplier makes it harder to mine blocks. It you are mining at x1 and find B blocks per hour, you would expect to find B/2 blocks per hour if mining at x2 with the same difficulty level.

There is an incentive to mine for a multiplier of at least x32: (2^5). Take a look at the code and you see some extra mining power added to make it a little easier for you to mine
https://github.com/bitcoinVBR/bitcoinV/blob/master/src/variable_block_reward.cpp