Shoulder strap adjustment

[AlfaQ]

By default I have always adjusted my bra straps so they are of  equal length without a thought. However my left shoulder and breast are slightly lower than my right side.  Tightening the straps on my left side to compensate for this has resulted in better support and fit.  It's amazing what you learn from utube.  

[Johndoe1]

Straps are intended to only support about 10 to 20% of the weight of the breasts. It's more intended to help keep the bra in place. The real support comes from the band and the smugness of the band. Breasts that are not as heavy or large do not require as large of a band. This is why it's recommended that the band be worn as snug as possible and still comfortable. In reality, that's going to be more snug than you imagine but the process is to keep the bra from moving during the day since the bra provides exoskeletal support. This is why proper sizing and wear is important for best and comfortable support. The bra must match your body's contours for that support. It can be a complicated dance between band, cups and straps to achieve that support and why there's so many type bras and why you need to try on a bra to see if it works for you. A bra that works for me is no guarantee it will work for you. 

[AlfaQ]

You are quite right about the underband being the main support of the breasts.  Shortening my left strap has helped smooth the  fit of the 3 section cups on this breast and eliminated the occasional strap slippage I experienced.  

[Justagirl💃]

You are quite right about the underband being the main support of the breasts.  Shortening my left strap has helped smooth the  fit of the 3 section cups on this breast and eliminated the occasional strap slippage I experienced. 

My right side as the shorter strap size for a perfect fit

[Johndoe1]

You are quite right about the underband being the main support of the breasts.  Shortening my left strap has helped smooth the  fit of the 3 section cups on this breast and eliminated the occasional strap slippage I experienced. 

For me my right breast hangs lower than my left and to keep the proper symmetrical appearance my right strap has to be slightly tigher than my left so both are lifted equally. Bras are really a marvel of engineering.

Sheri at Twin Sisters Mastectomy Boutique just did a YouTube short on bra straps. She makes some wonderful points. 
https://youtube.com/shorts/V3AlNrVtLrQ?feature=shared

[Parity]

That was good to hear. 
 I have been doing that without giving it much thought.  I figured that was part of the process of getting the correct fit.  I have looked at a few of my bras and they all have straps that if looking at are uneven.  When worn I look even.