I got a short intake (for 12/16mm hoses) for my 45-P thinking I would want to do some super high hardscape and any length would get in the way. I never ended up going too high, but the inlet worked perfectly fine (image attached for size reference next to drop checker).
The key to finding them is searching with the word "nano". The nano ones tend to bend back inward when they the go into the tank so they sit close to the glass wall, so just be sure your aquarium glass thickness is thin enough to work with it.
Here is on that's is 5.9" max height. You may be able to find it without the outlet if you already have that.
Amazon.com : JARDLI 13mm Glass Lily Pipe Inflow & Outflow for 12/16mm Tubing - Nano Aquarium Planted Tank Aquascaping : Pet Supplies
www.amazon.com
I would also look up ADA's DOOA line. They should have some small specialty inlet for their shallow tanks, but those will be pricier.