The chapter badge is placed accordingly to the codex astartes as shown in Insignium astartes on the left shoulder.
Termies got it on the right shoulder, cause
GW's old metal terminators had the crux terminatus on the left shoulder and
the shoulderpads of Termies are movable only with plastic termies.
Another point may be that the deathwatch sports its =I= on the left, so they have to field the chapter badge on the right.
Plus there may be chaplains with their badge of office on the left, so chapter is also displayed at the right.
( index astartes I - IV )
BT field their chapter badge on both shoulders.
So it seems Termies and some models with other insignia on the left shoulder field their chapter badge on the right.
OTOH, your sternguard sport Termie honors ( which no longer exist in the rules ), and these crux terminatus could been
accepted as always on the left shoulder. ( so veterans with crux = left shoulder, no matter if wearing
PA or
TDA ).
IMO, the fluff allows your config.