The A300 Outlander adjusts for stock drop and cast exactly like the 390, 391, and 3901 do, so if you find info on them, you can use it for your Outlander. There is a lot available here on SGW. For one thing, see viewtopic.php?f=57&t=101242
and scroll down to "Removing the stock, and using stock shims".
The adjustment shims change the cast to either "cast off" for right-handed shooters or "cast on" for left-handers. Each shim is marked DX on one side for cast off and SX on the other side for cast on. Select which one you need and turn both shims (the plastic one between the stock and the receiver and the metal one inside the stock) the same way.
IMPORTANT: Read the marks on both shims from the position of the shooter: don't make the mistake of putting the front shim on the wood and then reading the marks from the front. Make sure both shims are turned the same way.
Each pair of shims gives you two choices of drop. Drop is measured in mm of drop at the comb. The numbers representing drop are stamped on both top and bottom of the shim. Once you have turned the shims to the required cast (DX or SX), turn them so the number at the top of the shim (number is right-side up on the top, upside-down on the bottom) is the amount of drop you want. You may need to change to a different pair of shims. Again, make sure both are the same, when seen from the back of the gun.
Your gun is shooting low, so you need to get your eye higher when when you mount the gun to your shoulder, to make it shoot higher. You can do that by using a pair of shims that have a lower degree of drop: BUT before you change the drop, check the way you are mounting the gun.
You should not be looking straight down the rib. The rib is not intended to be used like a rifle sight. Your eye should be slightly above the rib, so you are looking down on it a little bit. Your Outlander does not have a second bead halfway down the rib like target guns do, but imagine that it does: if it did you should see the two beads lined up like a figure 8, with the front bead stacked on top of the mid-rib bead. You should not see the beads lined up so the mid-rib bead blocks your view of the front bead.
If you are forcing your cheek down on the comb of the stock in order to sight straight down the rib, it may be that all you need to do is change your mount a little bit. However, if your mount is comfortable, raise the comb by using shims that produce less drop at comb (a smaller number).