Re-reporting since nobody responded to my original post.
I noticed that my 159-character text message I typed into the site this morning was truncated when it delivered to my phone. The sender was "email@example.com " which is exactly as long as the number of characters missing from the delivered message.
I suspect this is ‘working as designed’ but also poor design, since many carriers include the sender info in the total SMS character limit, which means this will be an ongoing issue. Can the sender be changed to an actual phone#, or can the allowed characters be shortened, so full messages are delivered? (Ideally both - that’s a 33-character sender so reducing to accommodate allows less than the normal 140-160 characters for text messages, and everything we type into the form, we should reasonably expect to be delivered.)