Does limiting the amount of irrigation during the second half of flowering really help boost trichome production? If so, what would be the threshold based on? How much reduction in %?
Restricting water will not boost trick production. Over watering isn't good either. However high nutrient levels does harm resin. Cool temps and gentle feedings will boost resin. Not too cold or yeild is impacted.
Never starve your plants always give your plants the nutrient and water they need, starving them will only result in low quality and yield. The only time I starve them is the last couple days of there life. However they do tend to drink less the last week when growth has stopped and there just maturing and they can drink up water easier after being flushed and over watering can cause bud rot, so its safe to say you can cut your watering in half the last week and discontinue entirely the last couple days.
Do lower your humidy as much as possible the last couple weeks to encourage THC and resin production. Feeding your plants chitosan oligosaccharide is another great way to boost overall plant health as well as boosting terpine and resin production. Adding UV from a 10k MH the last couple weeks has also become common practice to boost THC, terp and resin production.
I'm growing outdoors close to the equator, so UV-A and UV-B rays are plentiful here. I thought I read that aside from aiding in pollination as an adhesive, trichomes also work as a sort of sunscreen by diffusing, reflecting and refracting light rays, so in times of extreme heat and lack of water the plant can limit transpiration.