complex subgraph

how to avoid overlapping arrows

I did a complex graph, with a lot of subgraphs and arrows accross subgraphs. You can find the .dot at the end of this message.
Nevertheless, I've got an issue with the arrows. In some aeras, I've a lot of overlapping arrows, as you can see in the attached file.
How can I structure the .dot file, in order to avoid this issue ?
Thanks in advance for your answer.

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