That 10x12 shooter plate dimension was so different from the ESAPI, I had to make a whole new pattern set for the Jungle Plate Carriers. The 10x12 shooter plate corners can be 3/4-1" wider each, depending on who made your plates, Hesco, Pacific Safety Products, etc, it is 1/4" narrower on both sides and at least 3/4" shorter in height.
The LBT-6094 has a generous plate retention flap inside that covers a range of plate types; the Mayflower APC has a 2" wide web strap with velcro to snug the plate against the top seam as much as possible.
The design and materials are asscrack/wrangler jeans tight, your only choice is to have a too small plate in a Large sized JPC. The nylon/lycra Tweave fabric panels on the backside probably won't even grip the plate, leading to it shifting all over.
Whatcha need, eh? A TW CadPat JPC, eh?