Looked at this myself, and I believe it deserves a larger drop.

Unsolds >=7

http://www.tf2outpost.com/trade/21538642 7.5

http://www.tf2outpost.com/trade/21519949

http://www.tf2outpost.com/trade/21504409

Solds @ 7

http://www.tf2outpost.com/trade/21550121

http://www.tf2outpost.com/trade/21528120

http://www.tf2outpost.com/trade/21515499

Solds/unsolds/selling <7

http://www.tf2outpost.com/trade/21547251 5.66, probably an outlier

http://www.tf2outpost.com/trade/21548475 6.11

http://www.tf2outpost.com/trade/21550317 6.66

http://www.tf2outpost.com/trade/21536718 6.66

http://www.tf2outpost.com/trade/21503024 6.66

http://www.tf2outpost.com/trade/21422925 6.88

Classifieds:

http://backpack.tf/classifieds/?item=Lumbricus%20Lid&quality=6&tradable=1&craftable=1

Several unsolds at <=7.

There are several 8 ref unsolds lying around though I didn't include them due to being outside of my proposed range.

In conclusion the range in the other suggestion is a bit too high, and my range is more representative of what the item is selling for.