"7,000 -> 7,500 is a 7.143% increase"
This is entirely irrelevant to this computation, an irrelevant detail. The computation is required to use the overall account value, not the value of any particular investment in the IRA.
See the definition of Adjusted Opening Balance and Adjusted Closing Balance in CFR 1.408-11(b):
https://www.law.cornell.edu/cfr/text/26/1.408-11#b
