It appears that you are using a version of T3?

Inter alia, T3 is based on the EMA(), which is an infinite impulse response (IIR) filter. Whereas it is possible to analytically, and rigorously, determine when residual effects from the starting value of an IIR become negligible, it is usually simpler to just specify an early enough starting index to ensure that the results are stable at your point of interest.