True, the fertilization makes sure much, but I also think that you should offer all year round warm humid climates to see really big leaves. Since 2007, I have a seedling of Anthurium ' big Bill', i.e. an A. (pendulifolium x cubense) x self. The great stands in the garden at around 12 ° C in winter and moderate to good air humidity, I have a Kamar at the living room window at all year round warm temperature, but rather low LF. Both grow very slowly no trace of Gigantism. Both have blossomed even, so no young plants.
However I seem to have caught not the best genetics, so anything can emerge from such seedlings. My plant has while the slender leaf shape by A. pendulifolium, but also the upright growth of A. cubense, so different as the mother plant.
If you need even more such monsters, A. spectabile and shelves I find A. also very sexy...