Creating Icons that work OK with both BC and Nav Unit


I am quite OK drawing with PS cc.
I understand the magenta requirement on my Garmin Nav (2820)
No problems there or with loading GPX data bases with correctly named icons. Using Garmin POI downloader which loads into Extras.
The 2820 is fine using 24x24. Any bigger get truncated.

Basecamp took a little more time but a png "save for web" with the correct settings did the trick re. transparency in BC. 48x48 , or even bigger works.

Now the Question.
Using a garmin icon wpt_0.tiff ( Anchor ) IDS_GDB_21 which happens to be 48x48 and using the transfer settings from within BC which loads into Favorites, the icon displays fine in the Nav.
Just trying to maintain compatibility between Computer and Nav take things simpler in the long run.
What I'm trying to do is load my icon with the GPX file to the list in BC