Ken I'm not tryin to be a jerk to ya so don't think that, but I simply think your are missing the fact that just because it is a 1" hose...that does not mean there is not a reduction in the system even from the factory.
Case in point I just took the elbow off one of my FX5's to show you what I mean. This is actually 13/16" here in the pic, and as it makes the turn it actually looks to be a tad smaller than 13/16". So just because the adapter is 1" to 5/8" that doesn't actually mean we are cutting the flow by 3/8" because there are other spots in the filter/factory equipment that are less than 1" from the factory to begin with.
See what I am trying to say?

Greg you do want to keep them as vertical as you can. I have mine pretty much vertical on both my 55g tanks. They are maybe 20 degrees tilted but no more than that.