I thought my backache would be helped by a more upright position on the bike so I flipped the stem and put as many spacers under it as I could. It didn't seem to help much... Then I went on holiday and borrowed an identical model of bike the same size as mine, but that one had a different set-up which felt more comfortable. When I got home I fitted a longer stem, did NOT flip it and moved most of the spacers to above the stem. It gives me a lower, more stretched out position which feels more comfortable to me.
Before and after positions illustrated below
View attachment 533321
(I have moved the saddle forward again since the lower picture was taken.)