Hi,
The actual display size of the tcp_idxbg.png in the theme you are working with is likely specified in the WALTER code found in the rtconfig.txt file.
For example, here is the line in the rtconfig.txt which I use:
set tcp.trackidx [390 5 18 18 0 0 0 0 ]
These numbers indicate that the tcp_idxbg.png is to be displayed as 18 pixels wide x 18 pixels high, and the top left corner is 390 pixels to the right of, and 5 pixels below, the top left of the Track Control Panel.
You can refer to the
Themer's Guide to learn more about the WALTER synatx.