Frontlever stalled - advice would be appriciated

I have a stalled frontlever at the flat tuck -> straddle. I am able to hold the flat tuck for 40 seconds in one single hold. However I cant even hold the straddle for 1 second. I can hold a flatback and a 45 angle between back and legs for 10 seconds or so. My main problem or weakness seem to be the teres major and minor muscle (Just below the deltroids and beside the posterior, away from the spine). First of all its these that get sore after workout, and I can feel its these that give up when I try to test the straddle.

Is there any excersie for the teres muscles I could do to assist the progression ?

Any other advice to shoulder position would be helpfull. Currently I just have a natrual position as i would if i grabbed for something. I try to push down on the bar and keep to 50% maximal work sets.

1-Leg Front Lever is where I have spent the majority of my time in training for the Front Lever. Its difficulty is between Adv. Tuck and Straddle.

I found the front lever currently the best exercises for teres.

Just try FL pull ups (tucked) and FL pulls. Those help a lot with FL. And of course negatives. Try straddle negative aswell.