No difference due rank. Basically, you get 90% of the ESF rate. If your child goes to an international school (most expat kids do) CX will cover 75% of these fees, as long as that amount is higher than the 90% ESF rate.
Most international schools are around twice the price of ESF. The allowance is taxable(16%). So after tax, ESF primary will cost you around $10K HKD pa. At an international school up to $35K HKD pa out of pocket.
These amounts don't include non refundable charges/debentures etc. Also does not include bus fares which I think amounts to approx $1 - 2,000 a month per child! You will find the schools that have the most ancillary charges have the shortest waiting lists! DBIS used to have a 3-4 year waiting list.