JCL - could you help me out again, please?

I still don't seem to have a proper handle on the Z8 Capital slider.

As before, the account is an IB nil margin, cash only account. AssetsZ8.csv is edited with leverage everywhere set to 1.

Trade run method 1:
- No positions open, cash only in the account
- USD cash on IB = $4238.42
- Capital slider on Z8 = 4238
= Z8 Result: Total volume $3367

Only about 80% of the cash available would be invested if I clicked "yes".

Trade run method 2:
- As method 1, but Capital slider = 5298 (ie. 25% above cash on IB)
= Z8 Result: Total volume $4118

It seems that only by doing method 2 can I get 100% of the available cash invested.

What am I doing wrong? Is my assumption that Z8 should invest all the cash up to the slider set amount wrong?

Thanks again, and apologies for what is probably a dumb question.