In most cases you will be seated at a 4 top although there are a few restaurants that have tables for 3. We've been seated at 3 tops at Boma and 'Ohana.
The dining reservation system has a known quirk that makes it harder for odd numbered parties (1-3-5 etc) to book. The system wants to fill every seat at a table so even though you will usually be seated at a 4 top, when you input "party of 3" the system skips over available 4 tops and shows no availability. Look for a party of 4 and suddenly you have a better chance of finding a reservation. As long as at least one person shows up for the reservation, you will not be charged for the "missing" person. Just be sure to include everyone in your party because of fire code regulations so go up to 4 rather than down to 2 when you are searching.