How can i predict whether or not the AI will attack into my forts?

Played some defensive games recently and i still can't guess the AI behaviour

Playing as Democratic France, i built level 6 forts on Netherlands border and the Germans never attacked there, but playing as Netherlands i built level 6/7 on German border and they lost 1 Milion man (to 100/200k if i remember correctly) in over one year of pushing unsuccessfully, even after French and British soldiers arrived at the front

Playing as USSR i built level 4/5 forts on all polish border and the Germans attacked into them (i had 5 armies of fully equipped and fully trained divisions of 7/3 infantry on that front) for more than a year, gaining only less than 10 tiles and losing 1,5 milions, but when playing as Communist Italy (i puppeted russia) i only had lvl 1/2 forts on the border with Poland, and 2 armies of untrained 7/1 deployed there and despite the stronger and slightly bigger army the Germans attacked into them for only a couple weeks (making small but significant advance) before stopping the offensive forever (game lasted for 3 more years before quitting) I must say that i declared on them in 39 (so they had 3 fronts open and never capitulated France) but they were still trying to attack Italy (they were attacking into lvl 3 mountain forts wtf) and france and also my troops got miserably defeated the few times i tried to counterattack. Basically i couldn't attack into them and they never did the opposite, basically an ethernal stall. But if i could have predicted the AI behaviour i could have tried a different strategy