[A Level] Monochloro Isomers

Hello everyone, hope we're all having a wonderful day.

I've already sat the exam but I've come across this question and can't let it go...

Here is a screenshot of the question in question: ( ...wait... )

I've put some annotations on the diagram so it can be easily referred to later.



Question 03.5 (not shown) states: "Deduce the number of monochloro isomers formed by isooctane. Draw the structute of the monochloro isomer that exists as a pair of optical isomers."

I got the structure fine but I got the wrong number of monochloro isomers. The mark scheme says 4 but I obtained 5 as follows:
1) A chlorine atom replaces a hydrogen atom on A or B or C
2) A chlorine atom replaces a hydrogen atom on F
3) A chlorine atom replaces a hydrogen atom on G or H
4 & 5) If a chlorine atom replaces one of the hydrogen atoms on carbon E, then carbon E will become chiral. So this accounts for two isomers.

I suspect the problem lies with my logic for carbon E but I would appreciate it if anyone could check me here.


For reference, here is a link to the paper:
http://filestore.aqa.org.uk/resources/chemistry/AQA-74052-SQP.PDF (Question 03.5 on page 8/9)


Thanks in advance!