Last question, what is your return pump model and flowrate.
Your chiller pump is rated 2400l/hour.
Your return pump had to be much higher than 2400l/hour as there is head loss.
You mentioned if you change to skimmer compartment, the water deplete very fast. I seriously suspect the final return pump turnover is lower than your Eheim 2400l/hr.
For your info:
My chiller pump and return is in the same last compartment due to space constraints but my last compartment is 1.5' by 1' by 1.5'.
I tried to put the chiller pump at 1 end of the compartment and the outlet from the chiller to the return pump area (in the other end) to minimise the same chilled water going back to chiller.
My chiller pump is at 2000l/hour while return pump is Eheim 1262 which is rated 3400l/hr, should be around ~2800l/hr(estimated only) after the 1.8m headloss.
At least this way, my turnover for my sump (last compartment) is larger than the chiller feedrate. Although not perfect but it is the best i can have.