that article was NOT about low flow restriction
you are correct re the 90^ ells, absolute flow killers
figure out how to fab one using the drawn copper soldered joint 90, or better yet, if it will fit use two 45s
(professional plumbing supply houses have a much larger selection than Home Depot)
and NEVER cut copper tubing with a tubing cutter as shown in the article
LOOK at the cut end, it is swedged down (the OD and ID reduced) and even worse it has a thin edge protruding into the flow
cut the tubing with a hacksaw and chamfer the ID edge (knock off the sharp corner)
details add up - particularly with a low-head pump
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