Speaker distance

It depends on the speaker design.  In the vast majority of speaker designs the ideal listening position is "far field" about 120% of the distance between the speakers.  So for easy math, if the speakers are 10' apart the ideal seating position 12' away from the speaker.  There are some speakers that are designed for "near field"  listening where the seating position would be less than 100% of the distance.  These are usually studio monitors or speakers designed like them.

This is just some very basic information and a good starting point.  The individual and unique room acoustics will greatly affect the ideal position but 120% is a solid starting point.  Good luck and cheers.  

Typically a rough equilateral triangle is best. Which every configuration gets you close to that. As @Rick_n there is some variation... 120% sounds good... 

Major variables are how far from the wall and side walls. Corners reinforce bass, few speakers perform well up against walls. Most speakers sound better with space to breathe. 

In my small room 8'h x 13.5'w x 9'd, I like the speakers set up on the long wall. Tried it both ways over the decades. 

See Jim Smith excellent book on getting the most out of your audio system - Jim setup thousands of systems over many years and makes specific process recommendations on how to get to best position in your room. Jim has sadly passed but his legacy of knowledge lives on…. Get the book

Here is a YT Video on the subject by Mr Smith. https://youtu.be/CX9y40bPkGI?si=0_BpDmadPmD6BH6-