To follow up, John emailed me directly asking how to treat
=COUNTA(D3:D29) and =AVERAGE(H3:H29) in a similar way.

There are a number of functions that can be used with SUBTOTAL(x,range)
- some of the common values of x a

1 - AVERAGE
2 - COUNT
3 - COUNTA
4 - MAX
5 - MIN

9 - SUM

You can use Help - SUBTOTAL_worksheet_function to find the other
values.

Pete