Yeah, you pretty much have it the whole concept down.
Typically, overflows that have more than 1 U-Tube we try to closely match the return pump GPH
to the overflow capability to prevent one of the siphon U-Tubes from collecting air (which does happen, I didn't match mine properly and I have to watch things all the time).
With the pump to help maintain the siphon, you're less likely to fall into this scenario, however, from my experience there's 2 things to be mindful of:
1) the siphon maintenance pump failing
2) believe it or not, when the siphon U-Tubes lose siphon and fill with air, the float up in the water. If this were to occur, the pump would not be able to reestalish the siphon, and if you're return pump is greater than what 1 U-Tube can handle the result is an overflow.
Personally, I will never again utilize a HOB
siphon style overflow, because of these types of issues (I have overflowed my tank on more than one occasion. once I was out of the country when it happened and my poor wife had to call a really good LFS
My next opportunity I will reset my non-RR tank by drilling and installing gravity feed overflows, similar to those from glass-holes.com, but that's just me.