I don't have a trainer but, wonder why do you have different size blocks you can set the front wheel on while using the trainer. Is it you are trying to simulate the angle the bike may have going up a hill? Or does putting taller blocks under the front wheel somehow create more resistance?

Nope when your bike is in a trainer, the back wheel is lifted from the ground. Every brand has its very own amount of 'lift' so to speak. The front wheel support or block as you call it, is made to level out your bike. That's also why every brand has it's own, to accomodate to different amounts of 'lift'. Although in some cases this differences are minimal.

To keep carbon forks from asploding.

It is "supposed" to give you that climbing feeling and help work those specific muscle groups. I simply use a fat metro phone book.

99% of my trainer use is to warm up for races. You may not be able to find a perfectly flat piece of ground to set up, so having options helps.

I prefer a little lift on the trainer as it feels more comfortable. Maybe it's taking the place of the air resistance that would be pushing on your torso.

Thanks, for the info folks. On my rollers I would guess my front wheel is probably 2-3 inches higher than the rear wheel. This is due to the rear being between 2 rollers versus the front being on top of a roller. I wonder if I have anything to gain from leveling the bike up on the rollers? In other words raising the back of the rollers. It may be if the front wheel was the same level or lower than the back the bike may be more prone to going off the front of the rollers.

i wouldn't mess with the rollers. it's like that so you don't roll off the front during a hard effort. just ride them on a flat, hard surface.