Alpine Stars Roost Reflector.

I dunno but buy this and send in a pic please

If you are a minimalist with chest and back protection, Alpinestar is not your go to.  Search other brands for what you are looking for like Oneal, the Split Chest Protector, the back piece can be removed and use the optional back strap. 

I don't believe so. I have the A1 Pro, which is a full back. I think when it first came out, Keefer did a review on it and modded the back from a previous model to have just the strap on the back. I mainly use the A1 Pro if I race or am somewhere crowded etc and wear it over the jersey. I have a Thor Sentinel with just the strap on the back that I wear the other times. I usually put it under the jersey put sometimes over. I probably wouldn't race in it though, as it is pretty minimal.

I don't believe alpinestars has a good version of what you're looking for. 

Not that you asked, but if you want an alpinestars chest protector without the bakc piece, the fly revel lite ce is a straight copy of the old astars a1 and you can remove the back. I would look into that one. Just my unsought $.02

EVS makes one, its called the Revo 4

Try searching for a Roost Deflector, you will find many options.

It's much more common than a roost reflector.

Supposedly 2026 any AMA race everyone is required to wear a chest / back protector. 

It's the A-4 Max, but it looks like he removed the back protector on it. It's not meant to come off.

Just SX (and maybe MX?) Futures that I am aware of, not at the true amateur level.