iPhone 15 pro max image format compressions

I’ve just done a number of tests with ProRAW, JPEG, HEIF and HEIF max. As discussed everywhere, and as you would expect, pro raw is the most detailed. To me, subjectively, JPEG is next, HEIF Max, then HEIF. The difference between JPEG and HEIF is quite small, but I plan to stick with JPEG (most compatible) as my switch between RAW, and ‘not RAW’ (slash) on the camera panel. In the format definition of the camera settings, JPEG is referred to as “JPEG Max”. Various levels of JPEG compression are referred to in different ways in different cameras. My question is – the main sensor produces a 48 megapixel raw image. The format for JPEG has“JPEG Max, up to 48 meg pixels“. What does this compression actually achieve? Clearly you can’t adjust the JPEG compression, so what is the fixed JPEG compression that is performed by the camera? An image taken in pro raw comes out at 72 MB , an image taken in JPEG Max comes out about 7 MB. But what is the actual JPEG compression? What does the max mean after the JPEG title?