Behind the Neck Press: Pushing Up and Back as a Sign for Good Mobility?

Hi,
so today I tried the BTN press for the very first time, going very light - did 5x10 sets, the heaviest ones were the 4th and 5th at 26kg (57lbs).
It felt good, but I asked one of the trainers to check me anyway on the last two sets.
Long story short, he told me I was doing it wrong - pressing up and back instead of straight up, and I didn’t push my neck forward.
He helped me to fix the form, but the thing that left me confused is that he said “it’s weird you can go that much back, you have crazy mobility”.
I had to deal for a year with a slightly rolled forward right shoulder for which I did a ton of mobility work and a ton of back work, so I’m curious: is being able to press behind the neck up and back really an indicator of good shoulders mobility?
I understand it’s not the right form and I won’t do it anymore, but I’m interested in knowing if that statement is true or maybe just exaggeration.
Also, I know people usually go just under the ear with the BTN press, but would it cause any issue going down to the traps at each rep?

Its a good movement if you can do it without pain. Some guys can work up to sets of over 300lbs, they usually are genetically blessed with shoulder joints that structurally are unlikely to cause tendon impingement.
I used to be able do them when I was young, but they cause trouble now. 57lbs isn’t much though, but you are right to break into the movement slowly and work you way up in weight. When you start to add weight its easy to sacrifice form for short term ego boost that you are lifting big weights(but not safely).

A safe bet when going heavy is not to lower the bar any further than having your forearms at 90 degrees to your upper arms. This mean the bar might stop at the level of the back of your head, around the top of the ears, not low down on the traps.

I’m not a fan of leaning your neck forward. Causes too much strain on the spine and leads to bad posture.
Pressing up and to the back is a good sign of mobility in my books, but once you start adding weight it won’t be as noticable.

Long story short, if it doesn’t cause joint pain during or after the workout, it means you can get away with the movement, regardless of what any average local trainer says.

If you have a smith machine try and adjustable bench. Try the highest incline setting just below 90degree angle. This works shoulder well with out pressure on neck upper back.

Thanks a lot for all the inputs.
I don’t see myself getting that heavy in the BTN press since the plan is to keep it as assistance in the 5x8-10 reps range, but I’ll definitely creep up and start adding small increments.
I think you’re right when you say that increasing the weight will automatically correct the bar path to a more vertical line, it makes sense, I didn’t think about it!

You mean doing the shoulder press frontally at the smith machine while seated on a bench? That was the original plan, I’ve read about it in a T-nation article and I’ve done it a couple times, it works great, really isolates the shoulders since you don’t have to worry about stabilizing and bar path.
I do that one too with very light weights (usually pyramid down from 66 to 48lbs over 5x10 sets) in the same day I have overhead press or push press as the main lift - and it gets the job done, 100%.
Fun fact, this time I had to resort in trying the BTN press because obviously there were a couple of guys doing random embarassing stuff at the smith machine and I was running out of time

Wanted to update the thread, tried again with the BTN press, I upped the weight adding about 9lbs (66 lbs total) and in the previous days I practiced a bit with a broomstick and empty bar focusing on bar path. Bar path today was spot on, started from the traps, kept the head slightly forward and came back touching the traps. Done 5x10, worked awesome, thanks everyone