Thais don't have family name system until early 1900, everyone was named by short syllables like Daeng, Maew, Pu, Chai, etc. Once the family name system is introduced, the custom of naming someone using short syllables continues in a form of family nickname. The trend continues to today, thus Thais have a nickname that don't related to the full name.
Except in formal situation, everyone here would refer to each other with their nickname. Calling Thais by first name or family name is equally awkward (even more so for ex-nobles, who have "na $Location" suffix in their family name, e.g. "na Ayudhaya"). So yes, please have a "What should we call you" in your form.
Except in formal situation, everyone here would refer to each other with their nickname. Calling Thais by first name or family name is equally awkward (even more so for ex-nobles, who have "na $Location" suffix in their family name, e.g. "na Ayudhaya"). So yes, please have a "What should we call you" in your form.