Fast return to LTE_ nokia 3G

Hi experts ,

Fast return to LTE after supplementary csfb is taking more than 10 sec whereas after cs call it’s taking only 1 sec .
Smart LTE layering is enabled with all services and all triggers. Any other parameter I am missing here .

In log analysis I can see after ussd signalling end msc sending of end of csfb message but RNC not sending rrc release with redirect and after that ue continue with Rau and lac update