Stuck Moving from sPL/SE3 to sPL/SE4 - Form Check

For about a year now I've been working on progressing from sPL/SE3 to sPL/SE4 and I haven't been having much luck.  I've added three video below and a few notes/thoughts for each.  Any help would be greatly appreciated.  

sPL/SE3

This is my sPL/SE3.  I feel like this is done properly but maybe not.   

sPL/SE4 - Bad Forum

I recognize that this is bad form.  My lower back arches and my shoulders are retracted.  However, this is how I find myself when I try to open from the tucked planche.  

sPL/SE4 - My Best Guess

This is my best guess at how to get from tucked to open.  I am trying to keep my back flat and am trying to lean forward to open from the tucked position while keeping my shoulders protracted.  Clearly not there yet but I am wondering if I am on the right track.  If I am not, are there any exercises that can be done to help bridge from sPL/SE3-sPL/SE4 or can you help steer me in the right direction with opening the from the tucked planche.

Hi @Jon Thornham,

Your sPL/SE3 is looking good but I don't think you have mastered it yet because you are having a hard time doing a few seconds. Please point those toes. Master SE3 first before doing SE4. You need to make sure that you also have mastered the previous mobility like Bent Arm Half Straddle Planche. (good lean, core strength, glute strength - to be able to do SE4) My tip for you is to revisit the previous PE to develop and strengthen your protraction so that SE3 will be easier.

Excellent advice.  I'll move back and do some more work.  Thanks. 

my experience with this progression is that i managed to master it and remaster it like up to 4 months , my weakness was the glutus medium that was falling before i got tired from protraction , now i am in a half straddle planche and it feels more comfortable , try little sets like 6 sec of even previous progressions like plank leans.