There are too many variables here for me to give you reliable advice. In general, female G. ternatensis will only mate when the female is ready to lay eggs. You can tell that by the state of development of her sternal cement glands. Also, females "test" males prior to mating by showing some aggression. Given that you have a small G.t male, he could be in for a tough time unless she is really, realy primed to mate.
Then there is the physical difference in size. It is going to be rough for the male to turn the female and reach the gonopores. I've seen males succeed at doing this when there was a large size difference, but it isn't easy.
If it were me, I would first access the female's reproductive condition and if she were reproductive, I would set them up in a tank with a divider and not too much cover. After a couple of days, I would pull the divider and watch quietly with net in hand. If nothing happened, I would separate them and try again in a day or two.
Roy
Roy