For testing I tried to specify a buffer_capacity of "90TW" (since I figured that would be an insanely obvious change

Not sure if this affects any entities other than the inserter...but it seems to me that if a buffer_capacity was specified in the source that is higher than the 'seemingly needed' capacity it shouldn't be overridden.
btw you can use a 'k' to specify kilo but for the rest of the multipliers you must use the capital version ('M','G', and 'T'), just a bit of inconsistency I noticed.
edit: tested in 0.9.7 and 0.9.8