SL/PE11 - Struggling to keep legs straight

I just started SL/PE11 (windshield wipers) and I am struggling to keep my legs straight.  Keeping my legs straight on SL/PE10 isn't a problem.  What additional stretching do I need to do to help with my form?  More Jefferson curls or weighted pick hangs?  I'm open to any and all suggestions.

Besides Foundations, I am trying to do the three stretch series once each week plus HS1.  

Hi @Daryl White, can you please submit a video of your attempt on SL/PE11

Leo I will do so either tommorow or Saturday.  Thanks.

Daryl, where are you with your MN progressions? A solid HLL (PE7) is the minimum requirement I'd say...