No matter what size small HOB you find it will require cutting a larger opening in lid.What is the size of the light attachment opening? Thinking of skipping the aio and using Hob if I can find one small enough.
Had same idea using a HOB but on the DIY frag tank putting the intake tube into the corner overflow. Plug off the bottom and the return hole vs using as designed with mini sump.
I found these AZOO filters being used on a 5g Rock Flower tank (YouTube). Would go with the 150 for the higher 40GPH which can be turned down with the knob on the intake tube.
Both are super small HOB compared to others out there and available on Amazon, other sites. There are other small HOB but picked these for the left intake, floss/media area, overall size and reviews.
Other Amazon options: Aqueon, Aquatop, Nicrew, Tetra, SeaChem Tidal, Marineland, etc.
AZOO Mignon 60 Filter - 3.25 x 3.75 x 4.72 in 16GPH for 4g tanks Think EA brand on Amazon is the same.
AZOO Mignon 150Filter - 3.95 x 3.75 x 4.72 in 40GPH for 10g tanks