I don’t have a problem with the notion that Christians in Heaven can pray on our behalf. However, I do have a problem with the practice of speaking with Christians in Heaven and requesting them to pray on our behalf.
When a Catholic says that aren’t praying to a departed saint, but are merely asking that saint to pray for them, the Catholic makes an assumption that humans in Heaven aren’t limited as we are here on Earth. It seems like a huge leap to accept that humans in Heaven are able to communicate with every single person on earth, even simultaneously with multiple people on Earth; they would have to be somewhat omniscient.
Heaven is truly a mystery for us, and while I admit I don’t understand all that Heaven will be like, I don’t see why Catholics are convinced that speaking with people in Heaven is fruitful or appropriate.
Heaven is truly a mystery for us as you say. For me in particular, I don't spend much or any time doing that speaking -- I commune with God in prayer and in the Eucharist and as a Catholic that's good. Requesting saints to pray with you is additional praise to God.