We would recommend trying the following Chantelle styles which offer convertible straps to solve the problems you had with the 3951: Chantelle C Chic Sexy Spacer Foam T-Shirt Bra 3585 style converts to criss cross in the back, and Chantelle Sexy Push Plunge Bra 3646which allows you to criss cross the straps in the back.
Kelly from Brannen
The Sublime 3951 is a average figure bra and could cause the flattening you discribed. You may need to go up a cup size in this style or try the Chantelle C Chic Sexy Spacer Foam T-Shirt Bra 3585
which offers a different fit than the 3951. The cup depth is very important to how a bra fits, supports and feels. Since a 3 part cup works well you may want to try a full coverage T-shirt bra such as Chantelle Rive Gauche Full Coverage T-Shirt Bra 3286 orChantelle Pure Full Coverage Convertible T-Shirt Bra 3616
Renee from CA
We would suggested you try 2 other spacer styles from Chantelle: the C Chic Sexy bra 3585
and Icone bra 3858. Both of these spacer cup bras offer great support, a rounded shape and breathable cups. Both of these styles convert to criss crossing in the back and have a clasp to prevent the strap from slipping out.
Martine from Salt Lake City, UT
Straps that convert can be tricky when it comes to making sure they are secure in place. we would suggest trying Pure 3612 Memory foam t-shirt bra with a different clasp that lock in place on the loop.
CT from CA