How do i set up the plugin to only make high external walls decay outside of TC range? 
I want tc's to act as normal (in vanilla)

If I remember correctly, you set "Disable decay for all entities" to true, set "Exclude \"Other Multipliers\"" to false, then add the external wall to "Other multipliers".

i dont want all enities to not decay though, wouldnt turning on disabling decay for all entities do the opposite of what i want to do

Setting "Disable decay for all entities" would turn off decay for everything.

yes but i do not want that

Ok I might have misunderstood what you are looking for. Are you trying to get high walls outside of tc range to decay faster or something?

Because in that case you could just add high walls to "Other Multipliers".

yes thats exactly what im trying to do, thats all good! so do i change any other settings or no?