I am not a cellist myself, but I am in the process of composing a sonata for Cello and Piano. Its the final project for a composition seminar dealing with Cello, so alot of the basics of cello writing I've covered. One thing I haven't touched yet is thumb position, which I plan to use for a flourish passage at the start of the sonata's recapitulation. So, if the thumb remains in a fixed position (stopping Ab3 on the G string, in this case), what is a comfortable range of extension for the fingers?
Also, are there any sorts of figures made easier/ harder in this position (certain types of melodic or double-stopped intervals, for example).
I really appreciate the help!