The V created between the seats for storage is where I usually put my 22" roller..BUT I put it opposite me, so I can see it....this may not be possible if someone has filled their spot, but still good advice! :) ON Regional trains even 22" may not fit easily over head, so try to avoid putting the luggage at the end ( entrance) of the car on the main rack. If you do use cable to connect them.
If you have a woman in your travel party...this is the greatest thing ever! I have used it in France and Italy for many years...but get the 2 strap style not the little snap one... this bra stash attaches to both sides of bra, but I prefer to attach it to ONE side and tuck the pouch into the side of my bra so it stays secure, if I am making daily purchases, I just take this out and pay, no one can run off with it because it is tied to the bra strap! I use this for one credit card and cash, keeping the rest of my cash, cards and passport in an under clothing pouch that I never go into in public.
https://www.bedbathandbeyond.com/store/product/rfid-blocking-ladies-personal-stash/
I take a real camera with me so that I do not rely on my iphone as much, as that is the #2 thing theives want after cash....and it is very easy that phones are stolen off of cafe tables etc.
Definitely pack 22" or smaller suitcases with a day bag, no more! It gives you more freedom, and washing things out at night or in the morning is easy, or have hotel do it for you $$, or find a laundry place if your trip is more than a week. I use one of those microfiber gym towels ( Amazon or any sports store) to wrap my heavier shirts or jeans ( I travel to Italy in Oct) to soak up a bunch of moisture, then hang dry them.
I always put a thin light duffle bag at the bottom of my suitcase, just in the event that I buy a lot of stuff and I don't mind checking a bag on the way home, I put breakables in duffle and carry on wrapped in clothing.
Happy travels!