So, my party of 3-14th, 5-13th and one 10th level characters has an ECL of 29.25 and not the 15.5 as calculated by the penpaperpixel.org Encounter Calculator? That just sounds way too high, considering that they have a hard time with encounters in the CR 20 range. When I plan encounters using the 15.5 figure that the Encounter Calculator gave me , they seem to be more appropriate challenges for the level (a little low from a "use up 25% of party resources per encounter" standpoint, but I can work with that).
The encounter calculator I use is at penpaperpixel.org/tools/d20encountercalculator (sorry, not computer literate enough to post a link

). I believe there are others out there that are available for free (search for d20 encounter calculators). It has definitely reduced my encounter planning headaches.