Let me go over some basics on suspension. As if the basic stuff is not right no matter how much adjustment you do it will never work, Example it you front tire is at 10 PSI and the Rear 50 PSI do you think you can make the bike ever work right??
But everyone knows about tire pressure, the problem is everyone does not know about suspension, and must "gurus" do not bother to explain anything, a lot of times it is because the "gurus" do NOT KNOW.
My experiance is if they cannot explain it to you, run away.
First always adjust your spring, do not tinker with the damping adjustments until the springs are right.
Front sag with rider 40 MM range 35 to 50MM
Rear sag with rider 30 MM range 25 to 40 MM.
Do not do anything until the springs and sag are right.
Now if, like in this case you are bottoming the bike, do not rely on a zip tie to determind this, if it is bottoming you will feel it.
The way NOT to stop bottoming, is more preload and or more compression damping, while this will slow down the dive it will make the bike ride harsh and not absorb bumps.
The way to stop it is by raising the fork oil level.
What does this do, the oil level does not have anything to do with the damping, as long as the fork valves are covered in oil they will work.
What changing the oil level does is REDUCE the amount of AIR in the forks.
Remenber as you are compressing this air the PSI is building, just like more air in your tires, the morfe the forks are compressed the higher the PSI, the stronger the air spring.
This AIR is a powerful progressive spring, the less air the more powerful this air spring becomes. The great thing about the air spring is that is does very little in the first 75% of the fork travel, but when you approach bottoming out, this air spring acts as a second spring, holding the bike up. Without having to have a too stiiff steel spring.
When adding oil to do this it MUST be done in very small amounts, usually 10CC per fork leg at a time. A very small amount of oil will make a big difference.