I like this list a lot. My only gripe with it is that Standstill is quite weak at board parity. With only 4 factories, there will be seldom be incentive for your opponent to break Standstill at a time which will be advantageous for you.
How would you go about fixing the issue without dillluting the manabase?
You can't really fix this issue. Once you start adding Concalves, Mutavaults, or other manlands, you lessen the probability of having the right mana available when you need it most.