About Big Lipo that my first problem too.
I use 5600 lipo cannot put in my E4FS .
I shim with 2mm. like Mr.Pro10noob post . Can use big lipo easy.
But now my lipo it's not bubble . When it's bubble may be more shim.
I have 2 lipo for play drift it's not hard work for batterry.
1 lipo5600mah can play 30-45minuit to 7.4-7.2v and I stop.
And 2nd lipo can full charge in same time.
Not waiting can play continuos with only 2lipo 5600mah.
I use my lipo very long time. Now may be near to 1year. For 2-3days per week.
No bubble and flat case.
I happy my E4FS very much.