Good observations. You are correct. That is part of the progression VRW needs to go through. We currently do mirrors and slot switchers on a number of randoms/blocks. However, so far we have stayed away from doing that on blocks 5 and 6 since doing them incorrectly can cost a lot of time.
To date the time saved doing mirros and or slot switchers on those blocks has not been enough to offset the time lost resetting. That is beginning to change as we get faster in B slots. In the near future mirrors and slot switchers will be used as needed on all blocks and randoms. We are just not that good yet.
Jon