The golden rule for bedside tables is keeping the top surface within 5 to 10 cm...

https://www.cool-bookmarks.win/aiming-for-your-bedside-table-to-be-level-with-or-up-to-10cm-below-your

The golden rule for bedside tables is keeping the top surface within 5 to 10 cm below your mattress top. This makes reaching for your phone or a glass of water effortless while you are in bed