retention time shift

running a gradient method on a waters alliance system. the RT spec is 27-32 min. however the peak is coming out at ~23min way too early. new batch of mobile phase/new column used and the same issue. then we changed to another alliance system in the lab and the issue was resolved, peak is now coming into RT window. 

I'm making an assumption that this is something to do with the dwell volume of the system?  however could too systems show such a huge difference in RT because of this and if so how would you modify the gradient to account for it (see below). 

flow rate is 1.5ml/min, mobile phase A is 90/10 water/ACN with 0.03% perchloric acid. mobile B is 100% ACN with 0.03% perchloric acid. 

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