When I switched from speedloaders to magazines (yeah I'm that old) I put them where my speedloaders had been; gunside of buckle & carried them horizontal. I found this to be very comfortable & fairly quick.
When I had to add a TASER & COBAN mic, I had trouble getting it all on my belt. (I don't see how skinny people do it) I moved my mags to vertical at about 9:00 on my belt. This slowed me down a bit, but is comfortable.
I can't help but laugh when I think about reloads; 1 magazine is 3 shots less than the total I carried when I started.