What are the homesickness images in Yu Guangzhong's works?

The poet chose four images from his personal life, namely "stamp", "boat ticket", "grave" and "strait" to express his feelings. This image seems ordinary, but it contains full poetry:

Stamp (small)-Mother-child affection (long)

Boat ticket (narrow)-love (thick)

Grave (short)-the sorrow of life and death (great)

Strait (shallow)-homesickness and sadness (endless)