Race Max questions: speed limiter and battery

Hi all, I have two questions as a new Race Max user...

1) My max 20mph (measured with a GPS app, not going by the bike's display) is underwhelming so far, I can pedal faster than that :( I tried changing the P08 to 63 as suggested in other posts and elsewhere, but my P08 setting only goes up to 46, and then back to 0. I can't get it to 63. Any ideas what I can do?

2) What's the maximum size battery *case* this bike can take? I ordered a 48V 20Ah battery (the listing photo had the height of the case at 3.94", which seems to be exactly the same as the 48V 12.5Ah battery that came with the bike), but when the battery showed up, it was over 5" tall and obviously I couldn't even get it on the rail. Has anyone replaced the stock battery with a larger one, and if so, which one was it? There seem to be several sizes on the market...

Thank you!