Unfortunately I have not finished a new coupler height standard for AMRA, and no other overseas standard is close to the Australian prototype coupler height. The standard I will propose will use a height within the prototype variation. For 1:87 scale I would suggest a nominal coupler centre height of 8.7mm for QR narrow gauge.
AMRA standards http://www.amra.asn.au/standards.htm
I have just checked the coupler height gauge that I had made from scale interpretation of QR's HOn3.5 and strangely enough, the figure I have is 8.7mm rail top to coupler centre. Your AMRA recommendations and suggested nominal coupler height appear to be pretty right.