Someone once told me when you are snowboarding you should ride as low as you can without breaking/bending at the waist... and then get lower...
I rode +15/-15 centered at 23.5 inches about half of last season. The other half I rode +18/-15 centered at 23.5 in. These angles work for me. I am 5'9".
A general rule of thumb the winder your stance the lower you can get by flexing your ankles/knees. Also the more duck angle you set the lower you can get by flexing your ankles/knees. Try standing in your living room with your feet shoulder width apart pointing strait forward (just wearing regular shoes or barefoot it doesn't matter). See how low you can get by flexing your ankles and knees. Try not to bend at the waist. Try this again with a slightly wider stance and duck your feet out. You should be able to get noticeably lower.
I like the tip they provide about making sure your hips fit between your bindings.
How to Mount Snowboard Bindings: SnowProfessor - YouTube
How you set your bindings up can have a big impact on how low you can get while you are riding. Setting up a wider comfortable duck stance is a good foundation to solid riding, but it will also help you progress into switch.