I bought the mirror and wish it was more adjustable for the $100 i gave for it.My 23 trail came with it. It is a little high but it's not too bad.
Do you have a pic of your custom mount?I purchased a 8mm - 1.25 metric bolt about 3 1/2” long ( don’t remember metric length ).
Cut the head off, put a 120 degree bend in the smooth end at about 1 “. Then threaded the bent end with an 8 - 1.25 dye.
Installed it on the bottom of the factory shaft using a metric coupler. Also added a metric nut to each end of the extension to lock the adjustments.
Just the right height now. Gives a great view under the Honda Bag I have mounted behind the front seat.