It's pretty important that 1-x effects be geometric, rather than arithmetic.
Say you have a -10% attack time, and you allow this to be arithmetically cumulative. Building 10 of them would give you -100% attack time, aka instantaneous attacks. Clearly bad! Likewise if you added -25% for war plus -15% for tact plus -35% for rax plus -10% for godspeed plus -10% for quickfeet plus -30% from avian you'd have substantial negative attack time.
In another example, with GS and rax being 1-x, if you get 50% from guard stations this is not giving you a 50% bonus, but rather a 100%: enemy gains being cut in half. Long-term, a fix for this is making these into 1/(1+x) effects, so 50% from guard stations only gives 100/150 = 2/3 net gains.
Rather, these should be geometric. Particularly in the case of gains or attack time. If small effects are combined, simply multiply them. If larger effects are to be applied, an inverse geometric formula (e^-kx) should be used.