Controlled group, different plans/years - HCE determination

[Belgarath]

So, suppose you have CG, consisting of Corps A, B, C, and D. A & B sponsor plan #1, and they run on a calendar plan and fiscal year. C & D sponsor Plan #2, and they run on a 10/1 to 9/30 plan and fiscal year.

The numbers are such that either plan, no matter how you look at it, passes 410(b) and 401(a)(4) EASILY, as very few HCE's participate.

However, as an academic exercise for future reference, suppose you are testing Plan #1 (calendar year) and you wish to determine the HCE's for 2019. When doing the 5% owner test, are you looking at 5% owners only in 2018 and 2019, or, would an owner who was a HCE in plan #2 in the 2017-18 plan year by virtue of ownership in December of 2016 be included? Seems like it should be the former and not the latter. Same type question for compensation test - for Plan # 1, are you looking solely at compensation during calendar year 2018, and HCE status under plan #2 for the plan year ending 9/30/19 is technically irrelevant?

Maybe to try to condense the question, for plan #1, is the HCE determination made solely under the normal plan #1 timeframes (but taking into account all employees of all members of the controlled group)? I believe this is how it works...