on my printer there is a utility that has arrows and little light bulbs and you choose the option. the varnish needs time to wet out in order to become glossy. so whatever your printer offers, you'll be wanting the ink to be laid down, the lamp would be off trailing/behind the head or in effect the lamp is on ahead of the head direction. this means that the lamp is curing "coming back" not immediately after the ink is laid down. there may even be a "cure between passes" built into your firmware. but that is the general concept.