EGR Valve on a Fiat JTD - question...

[uncinquesei]

After a few months of sluggish performance, the occasional loss of power and general smokiness I fitted a blanking plate (restrictor plate really) to the 1.9 JTD in our Stilo. I did the usual scouring of forums etc and the car is loads better as a result.
BUT...
What I can't really get my head around is that the soot/ carbon / crap that had accumulated in the inlet port where the EGR valve connected had reduced the hole so much that I couldn't get my little finger in.
Surely, if the crap had restricted the port to that size it would pretty much be doing what the restrictor plate I fitted is intended to do (and does).
Basically, how does the restrictor work when the accumulated soot and gunk doesn't?

[finlo]

When they get clogged they usually stick in the open position, so your restictor plate is in effect closing it.

[finlo]

When they get clogged they usually stick in the open position, so your restictor plate is in effect closing it.