I don't have a silver dollar to test with Goes4Ever but I have altered my pattern also. There is some speculation that the factory (coin) pattern is designed for UK users and they don't have any coins that "hit" there. It has also been my experience that when sensitivity is too high there is falsing in this range due to EMI, so by having these coordinates rejected, falsing is slightly reduced when running "hot". Also, Large Iron that would read 35 Fe in all metal, "jumps" through the disc pattern and reads 1 Fe and that is why it has been disced out in factory setting, So the Iron will "null" like it should instead of chattering. A push of a button (quickmask) usually reveals it for what it is...Iron.
Like you, I would rather investigate the occasional strong Iron signal and determine for myself to dig or not. If it means I dig the occasional deep iron so be it...Ok so there's two ways I know of to alter your pattern to accept different objects, specifically the American silver dollars.
Tip: If you are editing your pattern indoors, turn your sens all the way down in manual.
The factory coins program pattern has a rejected line in the top right of the screen, presumably this is where silver dollars hit. To make certain you are not missing any of these low ferrous/high conductors follow these steps...press the menu button, go to the discrimination tab and scroll down to the edit function. Select with the right or left arrow key. Now you have the edit pattern screen. You will notice a column of squares on the left. This column determines how many pixels of discrimination you would like to edit at a time. For this particular pattern edit you can select any of the top three using the arrow key under the power key. (the bottom square is full screen edit)
Also, notice the column on the right. You will want to select the top edit function which allows you to manually move the cursor. The area to be accepted is
fe - 1, co - 43 thru fe - 1, co - 50. Use the arrow pad to position the cursor over these coordinates and press the accept/reject button to remove the "line" of discrimination (very bottom right button with the X and checkmark)
Another way to do it, would be to get a silver dollar and scan it from all different directions in learn mode. (if done with other coins you will want to use a "Big" edit square to allow for fluctuations) edit discrimination screen, highlight the third box down on the right column and highlight the second or third box in the column on the left. As you pass the coin over the coil it will automatically "open" the portion of discrimination where it "hits". be sure to pass the coin from different heights, angles, etc.. Be sure your sens is all the way at one so there is no falsing which will cause the screen to "open" up all over the place in learn mode.