Seated Press Without Back Support?

As my main vertical Press in my 5x5 routine?
I find that hard to stay in the groove with breathing and bracing (timing) with standing ohp.

By the way my goal Is to “powerbuild” i mean to get decentl big BY getting stronger at big movements. And once I build a decent foundation, bodybuild. In fact, I don’t care about specific lifts or about my strenght level per sé as I see strenght as a tool to get bigger (someone would say: stronger muscle = bigger muscle)

If it’s what you want to do, then go for it.

I do OHP this way because the ceiling in my garage is too low to do it standing. I can’t say it’s any easier though, and you still have to work hard to get the ‘groove’/timing right that you describe.

Biggest issue I find it if I let the bar go too far backwards it’s quite hard to save it, because you can’t just step back slightly to catch it.

I do standing OHP but with my bum and legs leaning against a bench. This way I find it easier to engage core and keep my form 100%.

What I’d do personally is try a few a see what helps get the best form/ mind muscle connection. I’ve always found seated better at a slight angle as well by the way (rather than bolt up right).

You’re gonna use and build more muscle and build more strength if you do it standing, especially as your big 5x5 exercise. If seated is all you have access to then that’s fine, but if you have room to do standing presses I would stick with that. I’m awful at standing press but still do it because the benefits outweigh the struggle. Seated pressing never made me grow like standing.

If this comes over as “harsh” its not. I’m 100% not being a dick. Just trying to get you to see things a bit differently.
What are your other options? If everyone told you - “this lift is only 10% as effective as the standing version. And should be preformed as a last resort” what could and would you do? As lcearly this is your last resort. This makes the whole question pointless.
And this is actually very freeing. You can stop worrying about “the most effective pressing movement” - you only have the one. So now you can give it 100%. No distractions.

As an FYI - if you stick training out for 5-10 years at no point will you look back and say “Wow - those seated unsupported presses really held back my shoulder development”. The comparison will be minor. In fact the seated version requires more core stability (for me anyway) so there is a lot to be taken from that.