black and white - B&W Negative Tray Developing: Uneven Development

Shooting on an old Graphlex Speed Graphic 4x5 using tray development I am having consistent problems with uneven development, noticeable especially in the skies.

Update: I get perfectly even development with either developer/time combo listed below when I use a tank.

I am developing in trays. My trays are 5x7, plastic and have channels, not ridges. I ensure my chemicals are always exactly 20 degrees celsius.

My normal technique (though I have varied this: see notes below)

1. 
   
   

   submerge the negative emulsion side up, and rock the tray 10 times each minute of development

   
   


2. 
   

   move it to a stop bath for about 1 minute with constant agitation,

   
   


3. 
   

   move it to a fixing bath for 4 minutes, rocking the tray 10 times each minute

   
   


4. 
   

   wash it for about 5 minutes

   
   
   


5. 
   

   submerge it in a quick wetting agent bath before hang drying it.

   
   

Variations I've tried that have resulted in uneven development:

• Films: Arista EDU 100 and Ilford Delta 100.


• Lenses: Ektar 127mm and Schneider Super Angulon 90mm.



• Developers:
  
  
  
  • Ilfosol 3 (1:9) at 5 minutes and 7.4 minutes
  
  
  • Kodak D-76 developer (1:1) at 10 minutes
  
  
  
  


• Fixer:
  
  
  
  • 4 minutes with fresh fixer.
  
  
  • Extended "re-fixing" for 10+ minutes with fresh fixer.
  
  
  
  
  


• Agitation: Periodic and regular agitation.

What could be causing this uneven development?

Scanned Examples

These are from a cloudless day. I've darkened them to emphasize the uneven sky.

1. Arista EDU 100, Ilfosol 3 for 5 minutes with periodic agitation.

2. Arista EDU 100, D-76 for 10 minutes with periodic agitation.