Why are some supplements taken with food, others on an empty stomach?

[jbuildyeah]

So I'm taking a few different supplements and I'm kind of confused as to why some need to be taken with food and others on an empty stomach.

First off, there's my fish oil softgels, which state they should be taken with a meal, but they (like most fish oil) are enteric coated, meaning that they stay solid in the stomach until they get to the intestines (to maximize absorption and minimize fish burps?) If the enteric coating actually works, why do they need to be taken with food? Don't they slip by the stomach anyway? Do they need to be taken with food because that stimulates the intestine to absorb more nutrients?

Then there's my pre-workout. Every pre-workout I've ever taken says to take it on an empty stomach. Does this have something to do with the caffeine or the NO-inducing ingredients? Or do I take this on an empty stomach so that it's absorbed into my bloodstream faster (ie, not waiting for other things to be digested/absorbed)?

My L-Tyrosine caps (which I take along with St. John's Wort for mood-enhancement) are supposed to be taken on an empty stomach and I've noticed that L-Tyrosine is sometimes part of pre-workout/creatine blends, but again, I don't understand why this stuff needs to be taken on its own. Creatine is actually the same way-- take it on an empty stomach or "first thing in the morning". Is there some reason for that?

I take my multi with meals, because I figure that if I don't take it on a full stomach, it might not get broken down and absorbed properly, but if all this other stuff works better on an empty stomach, am I potentially missing out on the absorption of some vitamins and minerals if I take this thing while I'm digesting other stuff?

Last but not least, I take a few caps of HGHPro right before bed (again, on an empty stomach).

Is there really that much of a difference taking one thing or the other when you're empty or full? Besides following the directions on the bottle (which I do) is there any way to tell when the optimal time to take any given supplement is? Should I spread my 3 softgels of fish oil throughout the day at meals like I do or take all three at once after dinner (or before bed!) I've seen people admit to both on here and other forums and I just don't know how I'm supposed to figure all this out because most supplement articles never talk about when to take them, only the perceived benefits and whether or not to take them at all.