First off, no excuses, when a female cycles and copulates, they do so, 24/7 for 3 to 5 days, SO you cannot miss it. Unless you go longer then that without looking at them. They also copulate right out in the open.
Also, males do not have to be bigger or have massive heads, not young ones. The statements you made are more accurate with older individuals.
The picture you show appears to have a young female who may be getting into condition(fat buildup). As soon as she does, she will seek a nesting area. She will dig burrows and cover them only to dig them up the next day, so on and so forth. Also at that time she will emitt pheromones and the male will copulate for the above mentioned time period. Then he will completely stop. Once the ovum drops and enlarges, you can easily see them in her belly. You can even count them. The closer she is to laying, the easier they are to see. As she gets near laying, she will use her last fat stores(in the skin) and viewing the eggs is so very easy. At that size, she normally will have about 8 to 12 eggs.
Depending on how suitable the nesting is, she will lay from 8 days to 30 days after copulation. Somewhere are that thirty days, the eggs will start to fail insider her and she will drop them.
Her job as mother is to hide her eggs from trouble and in a place they will hatch. So you better expect to dig the whole cage up. Heck, sometimes twice before you find the eggs. Many have have dug two, three times then found them(admit it RSG) hahahahahahahahaha.
You see the actual practice of making pretty cages with plants and all such, quickly changes when your successful. As they can lay eggs so darn often the cage never ever stays nice. Your constantly digging it up. If you continue to allow those things to reproduce, the cage will always be ruined. So somehow you have to stop them in order to return the cage to looking pretty. Monitors are the devils spawn, always ruining cages.
I have bred red ackies(and that is what you have) as young as 6 months of age and as small as 13 total inches. I have bred yellows at a grand total of 11 inches in TOTAL lenght. I have had many of the smaller species, V.kingorum, caudolineatus, storri, gilleni, pilbarensis, reproduce as fast as 4 months of age. That is, egg to egg.
So yours at 14 months and 16 inches are right in prime ripe condition to reproduce. Congrats of doing a great job with them. Cheers