Hi Holly, jb and CPA so close,
If it helps, here is a link to an analysis that describes the sec 351 nuances in more detail: https://scholarship.law.wm.edu/cgi/viewcontent.cgi?article=1057&context=tax
Specifically, page 2, sub-paragraphs ii and iii discuss both the treatment of contributors who provide both property and services, as well as the limitations thereon, (property should be 10% of FMV of services in order to qualify as part of the transferor group). These paragraphs cite the relevant authority as well.
In theory, if you had a situation where two people contributed 20k of property for 20% and one person contributed 10k of cash and 100k of services for 80%, the transferor group would still have control and sec 351 would still apply.
Treas. Reg. § 1.351-1(a)(1)(ii) effectively equates equates stock already owned and stock to be received for services contributed, so this threshold likely applies to both cases.
Also, for what it's worth, I doubt the CPA exam is concerned with testing at this nuanced a level. After all, it's supposed to be testing base level knowledge of an entry-level accountant.