Are cpanel webmail quotas included in WHM quota information?

Hi everyone, first of all, let me say thanks in advance for any information that anyone can supply me with. Anything that would point me in the right direction would be most appreciated, I'm very new to cPanel and WHM.

OK, so my question is this;

I have a WHM account, I then create a cPanel account from in WHM with 100Mb of space allocated to it.

I then create a webmail account in cPanel with a quota of 100Mb.

When I go back to WHM, I was expecting to see that my cPanel account is using 200Mb in total (I was expecting the 100Mb disk space that is allocated + 100Mb allocated webmail space allocated).

Instead, I just see one cPanel account with 100Mb space allocated. This confuses me for the following reasons;

1.) If a cPanel is allocated 100Mb it is classed as using this all (it has been allocated, therefor could be used if required.) It says 100Mb in WHM after all.

2.) If this is the case, why does the email quota not work the same way. I have still allocated a possible 100Mb which could be used if required, so surely this should be treated as allocated too?

In reality, this is causing me a headache as I have a number of accounts, all with different webmail accounts within. WHM doesn't seem to take the webmail quotas into account when it says I have used only 75% of my possible disk space, yet when I try to create a new account it says the disk is full. I thought this issue could be the results of this behaviour?

PS - I also just thought. What would happen if I didn't allocate a quota at all for the webmail accounts?

Again, thanks for any help, I'm struggling to work this out, and I've looked elsewhere online, nobody seems to mention this, so it must be either really obvious, or me being really stupid as usual.

Thanks.