It's too tight across the back.

背部太紧。

《牛津词典》

He gave the donkey a whack across the back with his stick.

他用棍子在驴背上狠狠打了一下。

《柯林斯英汉双解大词典》

He lashed the horse across the back with his whip.

他用鞭子抽打马背。

《新英汉大辞典》

She made speeches about flying. And she continued to fly by herself across the United States and back.

VOA: special.2010.05.26

She looks up at the telephone wires, and she thinks about all the messages, unintelligible, full of human longing, going back and forth across those wires.

她看着电话线，想着那些莫名其妙的，充满了人类欲望的信息电线上来回踱着步。

耶鲁公开课 - 1945年后的美国小说课程节选

was go to the bridge and walk across the other side and then walk back.

就是到桥上走走，从桥这边走过去再走回来。

鲜为人知的名胜 - SpeakingMax英语口语达人

Across the back runs a slightly polished metal band, the lone bit of stylistic indulgence here.

ENGADGET: Amazon Kindle Fire HD review (7-inch)

Exemptions do apply, such as if the car is not big enough to accommodate three seats across the back, then two will be sufficient.

BBC: Three children in car seats

The Tunisian side made their intentions of settling for a draw clear by stringing five players across the back, inviting Enyimba to come at them.

BBC: SPORT | Football | African | Esperance hold Enyimba