If there are multiple platforms at a location how does it select which platform to send to?
Just asking before playing with the mod.

Updated in 0.8.22: the default behaviour is now request-aware and conservative. Cargo ICBM will only send to a stopped platform at the target location if that platform has active logistics requests for the payload and the request import_from matches the silo’s source location. If several platforms match, it picks deterministically by available hub capacity, then platform name, then hub unit number. Platforms with logistics/request sections disabled, wrong import_from, no matching request, full hub inventory, wrong force, or no valid hub are ignored. If no valid requester platform exists, the pod falls back to the linked planet surface where possible, or is deleted with a warning for true deep-space misses.

There is now a runtime setting called “Platform targeting behaviour”. The default is “Request-aware requests”. Switching it to “Permissive free-space fallback” restores the older behaviour where a stopped platform with enough free hub space may be used even without a matching request.

TL:DR
"If there are multiple platforms at a location how does it select which platform to send to?
Just asking before playing with the mod."

pre 8.22 acted like a vanilla silo sending to the overhead platform, but treated all the sent items in rocket pods as if they were the automatic requests, like for repairing destroyed parts of the platform (these requests were not planet-specific and could request from any planet the platform was above).

Now it is treated more conservatively, requiring logistic group requests to be enabled like when you manually add a logistic request group and add item requests specifying the "import from" setting. You can go back to the more permissive system using a new mod setting.