OK, let's look at two approaches. The NDB ILS DME RW28 Manston, and the ILS DME RW27 Norwich.
Firstly, let's assume we're inbound to Manston. We're approaching from the north west, and we're flying on a heading of 140 degrees. We fly direct to our IAF, the MTN NDB. Once we're overhead the locator, we fly outbound on a heading of 114 or 120 degrees.
Now let's assume we're approaching Norwich. Again, we're approaching from the north west, and we're flying on a heading of 140 degrees.
Our IAF is the NH NDB. Once overhead this beacon, we want to position south of the final approach track. If we're been approaching from the east, we'd simply 180 (or near enough) once over the beacon, onto 092 degrees, and this would give us the correct distance to the south to fly the outbound leg of the procedure. It's then simply a case of turning inbound at 7 DME.
So AFAIU, it's easy enough to fly if approaching from the east, but what happens when you're coming from another direction.
This also asks the question, what happens when flying a tear drop approach (as in the Manston example above), and you have to 180 to be on the outbound leg?
Let's say we were approaching Manston from the south, to be on the correct beacon outbound heading, surely we'd need to start the turn earlier than the actual beacon, to be positioned correctly.
Reading back over that, it all seems very confusing, but hopefully you'll see what I'm getting at......!!
Cheers,
tKF