I have only played with Efke 100 a little bit and my gut feeling is that it behaves very similar to the old Agfapan 100 regarding development.
Ilfosol S 1+14 for 10.5 minutes should be good.
Thank you for your advice. I tried as you recommended, but the negative is too clear. Tomorrow I will try a longer time, or a different proporions water/Ilfosol. I keep in touch with you.
I'm in the midst of moving homes, so I don;t have access to my files to check how I developed Fortepan, Agfapan and others in Ilfosol-S.... sometimes during next week.