I'm 99% sure that that vast majority of federal congress people (which represent ~1 million people each) never see your emails/letters. Your largely speaking to interns/etc who work in the office unless you happen to make a physical appointment and show up in person.

Those interns have a pile of form letters they send for about 99% of (e)mail they get, and if you happen to catch their attention you might get more than than the usual tick mark in a spreadsheet (for/against X). Which at best might be as much as a sentence or two in a weekly correspondence summary which may/may not be read by your representative depending on how seriously they take their job.