The logic sounds right to me.  The "need" is generated today, when you enter the sales order.  So today is the "date required" and to receive it today you would have had to order it 30 days ago.  If you write a purchase order today, the due date should be 30 days from today.
 
MRP is designed to work off future events, driven by forecasts and scheduled work orders, purchase orders, sales orders, etc...   It can't make lead times shorter than what you entered.
 

Thank you Lynn, I will get it figured out someday. It is tuff in our business we only have a 5 day order board so we cannot base our MRP off sales orders, so I am forced to make forcasts based on past history. The problem with that is our product base is so large and we have very few products that are "standard".

Wrong
use the MRP for every item you plan on stocking, making, buying or selling
 
say you get an order for something you dont have in stock  (reorder level 0 reorder qty 1)
MRP will tell you to buy it and when based on how long it takes to get (lead time)  and the requested ship date.
 
 
say you keep 1 in stock you get an order for 1   reorder level 1 reorder qty 1
same thing will  happen
MRP will tell you to buy another one  so you dont run with an empty store
 
if an item is on a BOM that can be used even accidentally it should be MRP enabled
 
The only thing I might turn it off for is an item you will never make or buy again  never sell again and is disabled so you cant enter a sales order or work order for it.
 
MRP is like a magic window. Its your vision of the inventory. Any activity on any item that is wrong will make it show up on the MRP so you will see what is going on with things before they get out of hand. as you get to know your items assemblies ect you will be able to spot problems at the start rather than the end of the process.
it wont solve every issue or catch every mistake but when the MPR says BUY or MAKE you will at least be flagged that there is activity that will be costing you time and money. you review each item  (copy paste from the report via a spread sheet into IN-A) look at the item and then decide what to do  
 
fix it
buy it
make it  
or adjust it
 
treat every item the same.  NO " Special items "  a screw should be treated the same as a million dollar item.
 
MHO
 
J Dub

ALSO
if the need is covered by an existing PO or workorder  and its still telling you to buy or make.
 
you need it make buffers bigger
 
OR
 
you need to get the dates on the po or workorder fixed so they fit into the requirments of the buffers or delay parameters.
 
so Expidite those po's and workorders get stuff in on time
use proper dates on workorders sales orders and po's
 
things will smooth right out
 
J Dub