To raise your POI, remove both set screws and lower the rib. Screws must be installed in the same sequence (1st hole in front, 1st hole in the middle). Be careful with these screws, the head strips out easily.
There are two screws holding the rib onto the barrel. You must remove both screws and then move the rib in the direction that you wish to go. The screws have to be in the same hole on each bracket. To raise the pattern up, you lower the front of the rib. You will also find that you will need to raise the comb slightly. This will give you the same sight picture and effectively raise your pattern. If you wish to lower the pattern, raise the front of the rib and lower the comb. Bill Malcolm
First off, congrats on what appears to be (from your question) a new to you 90-T HPAR.
If you take a look at your barrel, you will find that there are three allen head set screws.
One at the rear on the right side, and two on the left side in mid rib and in the front.
Notice also that there are 4 holes in the mid rib and front.
What you do to lower the rib (which will raise your POI), is to remove the mid and front allen screw and (CORRECTION -> Do NOT loosen the rear screw). Then what I do is using the front of the rib, I move the rib up or down so that the next hole that the screw can go into is aligned. Put the screw in and then put the screw in for the mid rib hole. Tighten enough so that the rib does not rattle or vibrate, test this by closing the barrel. If loose, you will hear the rib kind of set up a vibration noise.
I have mine set all the way down, which means the screws are in the front most holes. This will provide you with the highest POI.
Now, some guys ONLY use the adjustable comb for their POI adjustment. Once they get that set, they may then adjust the rib to provide the bead stacking that they like to see, such as a figure 8 or some such.
Lastly, I do recall that some of the earlier 90T HPAR's did not provide a POI adjustment by the rib for some shooter's style or taste. Remington (The shop that made them for Remington is known today as Kolar Arms) apparently made adjustments to the HPAR adjustable rib to remedy this. However I do not know what that fix actually is/was. I suspect the hole location was adjusted.
In any case, I hope this helps you. I would not use ball end allen keys and take it easy on those screws so as not to mar them. You want a 3/32 key for the front and middle screws and a 5/64.
for the rear. I keep a fine set of Xcelite allen key drivers with the extension in the 90T gun case.
BTW, Doug Breaker is the guru of these guns from a smithing standpoint. He and others can probably add and or correct what I have said here....
Sounds like, from the last few words in Doug's reply, that he maybe, could, might, aught to have a skunk works project going on to fabricate a rib that raises the POI higher? That would be nice.
After all... He IS the Gun Doctor