I have no clue on the anatomy or condition.
1. This makes your input particularly valuable.
My Boston marathoning PT has some ankle issues, but says standing calf raises (BW singles) help him with them. Have no clue if will help, but just a thought.
2. Ah... You know someone who is a PT and who has ankle pain. That does increase your expertise considerably. Please forgive any sarcasm you may have sensed in #1.
Is the pain more there when you have bent knee (solues stretch)?
3. The OP has told us that his pain is nowhere near his soleus.
Have you tried Thompson test for achilles connectivity? (Jungledoc will be along to abuse me for suggesting this.
4. Here I am. I have no idea what "Thompson test" is. Here I must bow to your more prompt use of Google.
Then there's issues people can have with the plantat muscle and or the peroneals (more lateral though).
5. See #3, inserting "peroneals" in place of "soleus." Also, I don't know what the plantat muscle is. I did not get a perfect score on my musculoskeletal gross anatomy practical exam. Perhaps that's one of the ones I missed.
Could just be Achilles tendonitis.
6. See #3, inserting "Achille's tendon" in place of "soleus."
Also, see #1.