ORIGINAL: JimCasey
Chuck Cunningham's articles are the holy grail of RC float Flying. The main article is available in several places on the net. Randy Linderman got permission from Chuck himself to post it, so I still refer to that link. [link]http://flyinglindy.homestead.com/skisandfloats.html[/link]
Chuck puts the step slightly behind the balance point.
Within a month or 2 of Chucks article which appeared in RCM, Ed Westwood wrote a similar but more techie article in MAN. He says to put the step under 40% of the MAC. For those of us from Tennessee, that means slightly behind the balance point. [link]http://www.smilesandwags.com/Floatsite/westwood.html[/link]
Andy Lennon used a line swept back 10 degrees from the CG to locate the step. that still puts the step slightly behind the balance point, but it scales better.
I tried Ed's theories from the "How to" MAN article to test and set up few different models, I sure wish I would have held onto that issue.
I seem to remember Ed used a right angle off the afterbody up to the CG to locate step location relative to CG, not like you mention Andy's 10 degree down method, If you figure 3 degree incidence + 3 degree afterbody angle it ends up more like 6 degrees not 10. 10 would shoot it aft of CG even further, but again depending on many factors, it still could work fine.
Optimum location (and workable range) of step and incidence angle can vary greatly depending on the model, A flat bottom airfoil Cub or Senorita like the OP's plane will be set up quit differently with a much wider workable range that a semi-symmetrical Scale plane like my Kingfisher or fully symmetrical Extra 230 I've built for example. The more rotation angle the plane needs to take off and land the more critical these angles and location become.
There's just not one answer for all air frames. You can't just say "always put it 1/X" infront/behind CG" Period, there are too many variables