I have further explored the issue I tried to explain in my previous post, as follows.
I have applied the VBA program to a range of consecutive whole numbers from 10 to 35.  The rows containing the numbers 10, 11, 12...15 returned my default row height: 11.25, but for the numbers 16,17..35 the program adjusted the row height to the respective number.  I then tried the numbers 35.5, 35.65 and 35.325 and the resulting row heights were as follows: 35.5, 35.75 and 35.5.  I suspect the "error" heights for 35.65 and 35.325 reflect the limits of sensitivity of the software.
Reverting to the issue of the smaller row heights; if I use Excel's manual row height adjustment function, the row heights adjust accordingly, within similar limits of sensitivity to those identified with 35.65 and 35.325. 
I suspect a parameter contained in my Excel 'Options' settings may be limiting the program's ability to adjust row heights less than 16.  Can anyone shed any light on this?
Chris