Farrow fractional delay filter - Range of delay?
Do you think this link could help you?

http://users.spa.aalto.fi/vpv/publications/vesan_vaitos/ch3_pt1_fir.pdf

I'm not sure I understand 100% of your problem, but IIRC when implementing fractional delays with say a FIR filter of 13 coefficients, you should stick with a group delay between 6 and 7.