If the siphon tube is made up of sections that snap together, and one of the joints is above your water line, air will get into the tube through the joint and eliminate the siphon. To overcome this, you'll need to glue/seal the joints. As long as there is water in the tube, I don't think the motor would be working much harder - every siphon is pulling in water from the bottom opening of the tube.
The issue is at start up, or if the power goes out. The water level inside the tank will be equal to the water level in the filter. If your tank water level is lower than the filter, then water will drain out of the filter until air gets into the siphon tube, breaking your siphon. When you restart, that's when the motor will chug for a bit until water gets sucked up the tube - IF it's powerful enough to do so. Otherwise, you'll have to prime the hob every time by refilling it during startup, which could get to be a drag.
The water in the well of the hob is what keeps the motor cool. If it runs dry, your filter will be toast shortly.
a half filled 55g wont be enough room for archers, if you get archers you need one , or a group 5+ , they dont seem to do very well in small numbers, your best bet would be to fill the 55 gallon and fassion a top that is quite tall, archers get stressed with a low canopy...