Not sure, but most nle overide the vts preroll settings, but…
to adjust preroll on the deck,
look at vt composite character out (the output with the tc display)
press menu on the beta frontpanel, or under the flap, this should display a menu on the monitor, you then use the jog wheel to scroll through the munu, preroll is probably item one, to adjust hold down the jog button whilst rotating the jog wheel to adjst the setting, then release and press the set button.
you probably need a preroll of 5 secs or more for a sp beta to lock, though 5 secs is probably the default on the beta.
Again, if you printing to tape the transport setting are sent over 422 to the deck overiding most internal settings so try adjusting preroll in you fcp dect configuration first.