The relevant model documentation describes decimal Modbus acquisition addresses as Base1 and hexadecimal acquisition addresses as Base0. BACnet forwarding object instances can start at 0. Check the selected driver, device register table notation and tag properties; a table row number is not necessarily a protocol address.
For the WEB configuration product mapping described in the X2View manual, 3X/4X address = BACnet address × 2 + 1, and 0X/1X address = BACnet address + 1. These are documented forwarding mappings, not a conversion rule for arbitrary acquisition-device addresses. Also check register type, data type and byte order.