Also, it depends on the congresscritter.
All members of the UniParty tend to just ignore anything coming from the “unwashed masses”. They’re nothing but cattle to be “milked” every April 15th.
I have been told privately by staff that 5-7 letters on a topic is the threshold to start a file. Meaning they are paying attention to see if really is of concern to the constituents. How many it takes to get the critter to take action they didn’t say.