It's truly simple to remove that nub. ATI even sells their 1590B's and 1590G's with it ALREADY removed now because it's so common. On N1's and A's it's typically not a big deal, same with P's, but on B's and G's that bottom right nub only serves to block parts / take up space. You can literally take a drill with a small drill bit and just drill right through that bitch. Then take a dremel with a grinding tool or a small file and clean it up. This will allow that battery to sit flush and straight with the side of the box and will overall give the box more internal space.
If the modder is unable to do this / refuses for some reason, this is something you can quite easily do yourself if it comes to it. It's just drilling down through that nub then filing / grinding it out to clean it up after. Takes.. 5-10 minutes tops.
This is obviously a case-by-case basis sort of thing, as sometimes you don't need to remove that nub. I usually have my lipo orientation facing down with the wires on the bottom, so even if I were to remove that nub on most of my mobs, the charging molex / butt of the XT60 wires would block the battery from going lower regardless. But in mods with an unmodified sled or a sled not made special for a Hammond style box, or in a mod like your mod where the lipo orientation is up and has the wires on top, it makes ALL the sense in the world to remove that nub.
I've made a lot of mistakes, but all mostly small. Having glue accidentally leak out when drying and stain the inside of an enclosure, get a hole SLIGHTLY off center and have to go back and clean it up to look center, a scratch here and there on an enclosure.. EVERY modder has this happen to them. But I've honestly never wired a mod up incorrectly and NOT noticed it while testing. I know the guy is new to PWM mods, but that is.. eh.
That's a BIG mistake to not notice, if you wouldn't have posted that there is every chance he would've mailed that out to you. In a form that basically had it as an unregulated 3S lipo mod opposed to a PWM mod, as that is what happens when you wire the pot in wrong. The mod assumes there is NO pot at all and just fires full voltage. There's no pulse switching, no timers, nothing. It is LITERALLY an unregulated mod in that configuration. A PWM mod with the pot at 100% is also basically an unregulated mod, but you have 1-99% to cycle DOWN through. A PWM mod with a botched pot doesn't have that option obviously.