Indeed and that is the reason why thicker tubing though-out the loop works better, the more volume your tubing has, the slower the flow-speed will be for the same amount of water passing through any point in the tube, and this is good, because it limits the formation of turbulence in the tubes.
This is exactly what you do not want in your block, for obvious reasons. And also why so many commercial block-Designers have missed to boat (by a mile)
Nowa days they are starting to get the bigger picture. you will be seeing a lot more restrictive block designs popping up everywhere, as already is the case......
The block need to be the only part that should offer resistance to the flow.... because it is the block that need to convert the pressure it sees from the pump, into violent turbulent flow through it, which is what makes a block perform well. Smooth open flow paths are not what you want in a block.
obviously a good design should then give you the smallest possible liquid-volume, for the biggest possible exposed surface-area. The best thing of it all, there are some designs out there that, once you get to that point, it actually also gives you the much needed turbulent flowpath as well...