Within SliQ's invoice template editor a number of types of condition can be set on a field. One condition type is the offset condition. The offset condition allows you to move the position of a field depending on the value of another field. See here for help:
The standard templates in SliQ use the offset condition to move invoice and quote total values depending on whether the business is VAT registered - moving the total field up to avoid a gap if no VAT value will be output.